Re: Terrestrial Switchoff - sorry to labour the point but...

[Stephen]

<ne...@address.invalid> wrote in message
news:u3jgk852e6nvj55fm...@4ax.com...
> For those who haven't yet seen the Ofcom consultation on future mobile
> broadband spectrum.
>
> "The 694-790 MHz band is expected to become a key band for mobile
> broadband"
>
> and references to studies at 470 - 694 MHz.
>
> http://stakeholders.ofcom.org.uk/binaries/consultations/cfi-mobile-bb/summary/cfi-mobile-bb.pdf
>

If they sold off the whole of UHF, we could go back using VHF for TV if we
just forgot about the regional news. Freeview only needs 6 channels for
single frequency networks and these 6 should be available on VHF Bands I and
III.

Only the regional TV variations need to be relegated to satellite, cable &
internet.

The VHF bands are much less attractive to mobile phone operators because of
the much longer aerials required (particularly for Band I) but they are
perfectly good for terrestrial TV, and a new VHF TV aerial would be cheaper
than a dish, and much easier to align. We might return to the days of H
aerials, X aerials and Band III Yagis, but with digital TV on VHF instead of
405 lines.

[Ian Jackson]

In message <MYF2t.110752$Lp1....@fx03.fr7>, Stephen
<ste...@sptv.demon.co.uk> writes

VHF (especially Band 1) is not best suited to off-air multi-channel TV.

For a start, Band 1 is very prone to long-range sporadic-E interference
in the late spring and early summer. Even well before the advent of
digital transmissions, many European countries had ceased TV on Band 1
because of such problems.

Then there's the problem of designing aerials with sufficient bandwidth
vs gain. OK, the Americans have such things, but they are generally used
for the reception of relatively strong downtown transmissions. I'm not
sure how good those used in Europe are (or used to be). I can't remember
if (for example) Band 3 aerials, covering the whole of 175 to 230MHz,
were very common.

There are only eight or nine 8MHz VHF TV channels available (3 in Band 1
and 6 or 7 in Band 3) - and it would be extremely difficult
comprehensively to provide the whole of UK with 6 digital MUXes in the
same way as the two analogue channels were provided. At best, the full 6
MUXes could probably only be provided in well-separated centres of large
populations. Elsewhere, the number of channels would have to be reduced.
Although this is not dissimilar to what happens at present, I feel that
the situation would be much more marked than we have at UHF.
--
Ian

[Bill Wright]

Stephen wrote:

> The VHF bands are much less attractive to mobile phone operators because of
> the much longer aerials required (particularly for Band I) but they are
> perfectly good for terrestrial TV, and a new VHF TV aerial would be cheaper
> than a dish, and much easier to align. We might return to the days of H
> aerials, X aerials and Band III Yagis, but with digital TV on VHF instead of
> 405 lines.

I doubt if the aerials would be that elaborate. With no ghosting to
worry about and the ability of DTT to work with a low s/n ratio I should
think the aerials would mostly be in the loft, and would be simple
dual-band omni types. An SFN would probably be VP.

Bill

[Bill Wright]

Ian Jackson wrote:


> Then there's the problem of designing aerials with sufficient bandwidth
> vs gain. OK, the Americans have such things, but they are generally used
> for the reception of relatively strong downtown transmissions. I'm not
> sure how good those used in Europe are (or used to be). I can't remember
> if (for example) Band 3 aerials, covering the whole of 175 to 230MHz,
> were very common.

Log periodics.

http://www.wrightsaerials.tv/aerialphotography/aerialingus/005.shtml

Half a log is better than no log at all:
http://www.wrightsaerials.tv/aerialphotography/aerialingus/007.shtml

Bill

[Peter Duncanson]

On Thu, 21 Mar 2013 15:46:01 -0000, "Stephen" <ste...@sptv.demon.co.uk>
wrote:

Hmm...

"Yes Sir/Madam. I know you have an old VHF aerial on your chimney, but
it's pointing in the wrong direction. Anyway, you need a High Definition
Digital VHF aerial."

--
Peter Duncanson
(in uk.tech.digital-tv)

[MB]

I am sure the telecom companies would just love to get the rest of the
UHF TV allocation so they could have people watching TV through mobile
broadband (at least in those areas served) and make yet more money out
of them.

[ne...@address.invalid]

I don't think anyone would want to go back to TV in Band I for that
very reason, however Band III would be suitable if the DAB channels
could be recovered. Now *there's* an idea!

[Woody]

"Ian Jackson" <ianREMOVET...@g3ohx.demon.co.uk> wrote in
message news:I053GvNh...@g3ohx.demon.co.uk...

\pedant mode on

There were five channels in Band 1 and eight channels in Band
III. They were only about 6.5MHz wide as against 8MHz used today.

\pedant mode off


--
Woody

harrogate three at ntlworld dot com

[Ian Jackson]

In message <kifl4l$dlg$1...@dont-email.me>, Woody <harro...@ntlworld.com>
writes

I'm talking about the potential channel capacity of Bands 1 and 3 for
carrying standard UK 8MHz digital MUXes (based on standard UK and Irish
analogue 625-line cable TV practice, and also off-air broadcasting in
Ireland), so what relevance does your admittedly pedantic statement have
to what I said?

\pedant mode on

The UK, the System A channel width was 5MHz (sound-vision spacing
3.5MHz), with Ch1 being a bit of an oddity because it originally started
life as full DSB vision (later being changed to the standard VSB
format).

\pedant mode off
--
Ian

[Ian Jackson]

In message <kifeqn$pma$1...@speranza.aioe.org>, Bill Wright
<bi...@invalid.com> writes

I've actually got an unused (box unopened) large American multi-element
Band 1-2-3 aerial. I realise now that, one day, it may actually come in
useful.
--
Ian

[Max Demian]

"Bill Wright" <bi...@invalid.com> wrote in message
news:kife7q$mo8$1...@speranza.aioe.org...

Isn't that what set-top rabbit ears are for?

--
Max Demian

[Bill Wright]

Ian Jackson wrote:
> In message <kifeqn$pma$1...@speranza.aioe.org>, Bill Wright

> I've actually got an unused (box unopened) large American multi-element
> Band 1-2-3 aerial. I realise now that, one day, it may actually come in
> useful.

There are some Band III tv aerials in my dad's loft. I'm selling the
house next week. They can stay there.

Bill

[Bill Wright]

Max Demian wrote:

> Isn't that what set-top rabbit ears are for?
>

Yes but modern sets radiate more RF than the old ones!

Bill

[J. P. Gilliver (John)]

In message <kifl4l$dlg$1...@dont-email.me>, Woody <harro...@ntlworld.com>

writes:

>"Ian Jackson" <ianREMOVET...@g3ohx.demon.co.uk> wrote in
>message news:I053GvNh...@g3ohx.demon.co.uk...

[]

>> There are only eight or nine 8MHz VHF TV channels available (3
>> in Band 1 and 6 or 7 in Band 3) - and it would be extremely

[]

>\pedant mode on
>
>There were five channels in Band 1 and eight channels in Band
>III. They were only about 6.5MHz wide as against 8MHz used today.
>
>\pedant mode off
>
>

In UK, yes, under system A. In most of the rest of western Europe, there
were three on I (IIRR numbered 2 to 4) and correspondingly on III, IIRR
numbered 5 to 12 or 13. (Systems B and G if memory serves.)
--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

Can you open your mind without it falling out?

[Paul Cummins]

In article <kigelc$ve6$2...@speranza.aioe.org>, bi...@invalid.com (Bill

Wright) wrote:

> There are some Band III tv aerials in my dad's loft. I'm selling
> the house next week. They can stay there.

Why? Clean them up and sell them as DAB aerials.

�50 to �100 a time :-)

--
Paul Cummins - Always a NetHead
Wasting Bandwidth since 1981

---- If it's below this line, I didn't write it ----

[Paul Cummins]

In article <kifl4l$dlg$1...@dont-email.me>, harro...@ntlworld.com (Woody)
wrote:

> There were five channels in Band 1 and eight channels in Band
> III. They were only about 6.5MHz wide as against 8MHz used today.

So that gives space for 4 digital Muxes in Band I, and 6 more in Band
III.

Sounds like someone has the right idea about getting rid of DAB from Band
3.

[Andy Wade]

On 21/03/2013 18:58, Woody wrote:

> \pedant mode on
>
> There were five channels in Band 1 and eight channels in Band
> III. They were only about 6.5MHz wide as against 8MHz used today.
>
> \pedant mode off

A c t u a l l y , dear pedant, I think you'll find that 405-line system
A used 5 MHz channelling, or perhaps I should say 5 Mc/s.

European 625-line is (or was) System B in the VHF bands and used 7 MHz
channels, not 8. This was never used in the UK of course. 8 MHz
channelling only appears at UHF, System G for the mainland and System I
(with 6 MHz sound and originally a wider VSB) for the UK, also used in
South Africa.

DVB-T (and -T2 AFAIK) have a 7 MHz channel option to allow use in the
VHF bands. Do any countries use this?

--
Andy,

[Ian Jackson]

In message <ar3m9n...@mid.individual.net>, Andy Wade
<spamb...@maxwell.myzen.co.uk> writes

>On 21/03/2013 18:58, Woody wrote:
>
>> \pedant mode on
>>
>> There were five channels in Band 1 and eight channels in Band
>> III. They were only about 6.5MHz wide as against 8MHz used today.
>>
>> \pedant mode off
>
>A c t u a l l y , dear pedant, I think you'll find that 405-line system
>A used 5 MHz channelling, or perhaps I should say 5 Mc/s.
>
>European 625-line is (or was) System B in the VHF bands and used 7 MHz
>channels, not 8. This was never used in the UK of course.

Some of the 8MHz lettered channels (A to J) were used for 625-line
broadcasts in the Irish Republic, and in Irish and UK cable TV systems.

> 8 MHz channelling only appears at UHF, System G for the mainland and
>System I (with 6 MHz sound and originally a wider VSB) for the UK, also
>used in South Africa.
>

The narrowing of the 1.25MHz VSB to 0.75MHz was first found necessary on
cable TV systems, when NICAM (on vision + 6.552MHz) was added to
channels which were on lower adjacent channels, and got totally
clobbered by the upper adjacent VSB.

>DVB-T (and -T2 AFAIK) have a 7 MHz channel option to allow use in the
>VHF bands. Do any countries use this?
>

Just a final point.....
Do any DTV TV sets or STBs tune to Band 1? I think they start much
higher (off the top of my head, around 130MHz?). If so, that's another
reason for not using Band 1 for digital.
--
Ian

[hwh]

On 3/22/13 8:11 PM, Ian Jackson wrote:
> Just a final point.....
> Do any DTV TV sets or STBs tune to Band 1? I think they start much
> higher (off the top of my head, around 130MHz?). If so, that's another
> reason for not using Band 1 for digital.

The ones I have seen start at 174 MHz (or the lower edge of Band III).
If you set them to a country where only UHF is used for DVB-T however
they start at 470 MHz.

gr, hwh

[Graham.]

On Fri, 22 Mar 2013 02:13:12 +0000, Bill Wright <bi...@invalid.com>
wrote:

True, but modern sets don't suffer from corona discharge from the EHT.
(remember the white vertical 'rope' interference on Band I)

--
Graham.

%Profound_observation%

[Bill Wright]

Ian Jackson wrote:

> Do any DTV TV sets or STBs tune to Band 1? I think they start much
> higher (off the top of my head, around 130MHz?). If so, that's another
> reason for not using Band 1 for digital.

We'd just need another chuffing set top box.

Bill

[charles]

In article <ar3m9n...@mid.individual.net>,

Andy Wade <spamb...@maxwell.myzen.co.uk> wrote:
> On 21/03/2013 18:58, Woody wrote:

> > \pedant mode on
> >
> > There were five channels in Band 1 and eight channels in Band
> > III. They were only about 6.5MHz wide as against 8MHz used today.
> >
> > \pedant mode off

> A c t u a l l y , dear pedant, I think you'll find that 405-line system
> A used 5 MHz channelling, or perhaps I should say 5 Mc/s.

> European 625-line is (or was) System B in the VHF bands and used 7 MHz
> channels, not 8. This was never used in the UK of course. 8 MHz
> channelling only appears at UHF,

My memory says that Eastern Europe used a 6.5MHz sound carrier at VHF.
System D, I think.

> System G for the mainland and System I
> (with 6 MHz sound and originally a wider VSB) for the UK, also used in
> South Africa.

and Hong Kong

--
From KT24

Using a RISC OS computer running v5.18

[Ar]

On 21/03/13 17:09, Peter Duncanson wrote:
> "Yes Sir/Madam. I know you have an old VHF aerial on your chimney, but
> it's pointing in the wrong direction. Anyway, you need a High Definition
> Digital VHF aerial."

A digital aerial can catch all those 1's and 0's, but an "analogue"
aerial can't..!? Cue same marketing scam as in early 1980's with
"digital headphones" after launch of the CD player.

[Peter Duncanson]

Somewhere I have a pair of headphones with "laser" in the name. They do
not send beams of light into the ears!

[John Williamson]

Generally designed to make the most of the improved HF performance of CD
players after the dull sound of cassettes. They did this by making the
HF even louder than it was on the already top heavy CD.

Painful, most of them were.

--
Tciao for Now!

John.

[hwh]

My uncle was offered a 'color aerial' decades back. And yes, we
continentals had color on VHF ;-)

gr, hwh

[Java Jive]

I am not aware that CDs are in any way top-heavy.

If recorded faithfully without any digital processing (which is
important to specify because digital processing is widespread), they
should have the same FR as the original sound, up to their cut-off
point of 22kHz. However, when processing is applied, it usually seems
to be either designed to boost the bass (not the treble) end, and/or
squash the dynamic range to achieve more instant 'impact'.

I think what may be going on here is that many previous analogue
systems were top-light. For example, IMS the top end of AC is limited
by the slow tape speed to about 16kHz or so, that of a Shure VIII
vinyl cartridge is around 20kHz, and although a good consumer
open-reel tape system at its fastest tape speed (19cm/s) could match a
CD's FR, it could never begin to approach its SN ratio, say 45dB as
opposed to 100dB. This significantly higher SN ratio of CDs also
allows one to hear fainter, higher transients in the sound that used
to be swamped by vinyl noise or tape hiss.

Thus, to someone used to an analogue sound, a CD at first hearing
seemed unusually bright in the treble, though one's ear adjusted
fairly quickly, after which, going back to the analogue source can be
almost painful. But, in the absence of processing (always
remembering), it's the CD that has the authentic sound - that is the
sound closest to what was actually recorded - not the analogue
systems.

On Mon, 25 Mar 2013 15:20:09 +0000, John Williamson
<johnwil...@btinternet.com> wrote:
>
> the already top heavy CD.

--
=========================================================
Please always reply to ng as the email in this post's
header does not exist. Or use a contact address at:
http://www.macfh.co.uk/JavaJive/JavaJive.html
http://www.macfh.co.uk/Macfarlane/Macfarlane.html

[Stephen]

"Ian Jackson" <ianREMOVET...@g3ohx.demon.co.uk> wrote in message
news:I053GvNh...@g3ohx.demon.co.uk...

> In message <MYF2t.110752$Lp1....@fx03.fr7>, Stephen
> <ste...@sptv.demon.co.uk> writes

>>If they sold off the whole of UHF, we could go back using VHF for TV if we
>>just forgot about the regional news. Freeview only needs 6 channels for
>>single frequency networks and these 6 should be available on VHF Bands I
>>and III.
>>
>>Only the regional TV variations need to be relegated to satellite, cable &
>>internet.
>>

>>The VHF bands are much less attractive to mobile phone operators because
>>of the much longer aerials required (particularly for Band I) but they are
>>perfectly good for terrestrial TV, and a new VHF TV aerial would be
>>cheaper than a dish, and much easier to align. We might return to the days
>>of H
>>aerials, X aerials and Band III Yagis, but with digital TV on VHF instead
>>of 405 lines.
>>

> There are only eight or nine 8MHz VHF TV channels available (3 in Band 1

> and 6 or 7 in Band 3) - and it would be extremely difficult
> comprehensively to provide the whole of UK with 6 digital MUXes in the
> same way as the two analogue channels were provided. At best, the full 6
> MUXes could probably only be provided in well-separated centres of large
> populations.

I don't think this is the case. They should be able to use the same 6
channels at all transmitters like National DAB. A VHF network for Freeview
could be designed alongside an upgrade to DAB/DAB+, using the same
transmitting aerials and the same transmitter sites.

It may only need 5 multiplexes as there would be no need to duplicate the 4
main channels (BBC1 HD etc) in Standard Definition as is done at present. No
duplication of DAB radio on Freeview VHF would save some more space. The
system could use the European 7 MHz channel standard to integrate with DAB
which uses the same standard.

It might work out something like this: Channels E6, 7, 8, 9, 10 for DVB-T2,
and Channels E5, 11, 12, 13, 14 for DAB+.

[Ian Jackson]

In message <Ax14t.231508$Dm1....@fx01.fr7>, Stephen
<ste...@sptv.demon.co.uk> writes

Because of the need to prevent co-channel interference, it took five
Band 1 and eight Band 3 channels to provide two nationally-available
405-line analogue channels. OK, digital may be more resistant to the
effects of co-channel, but it seems extremely optimistic that five
adjacent channels at the bottom end of Band 3 could provide five MUXes
nationally. If it were possible, surely they would already be doing this
in Band 4 (say channels 21 to 25), leaving the rest of Bands 4 and 5 for
'other things'?
--
Ian

[Stephen]

"Andy Wade" <spamb...@maxwell.myzen.co.uk> wrote in message
news:ar3m9n...@mid.individual.net...

> Andy,

Australia does. They appear to have all their major networks on VHF with
DVB-T in 7 MHz channels. Also Potsdam in Germany.

[Stephen]

"Ian Jackson" <ianREMOVET...@g3ohx.demon.co.uk> wrote in message

news:YvwDQtEf...@g3ohx.demon.co.uk...

AFAIK DVB is designed for single frequency network operation but it wasn't
implemented initially. I think they intend to use it for some future
mulitplexes.

[J. P. Gilliver (John)]

In message <6bc0l8djv8ap00q6f...@4ax.com>, Peter Duncanson
<ma...@peterduncanson.net> writes:
[]

>Somewhere I have a pair of headphones with "laser" in the name. They do
>not send beams of light into the ears!
>

No; with some of the target customer base, it might come out the other
sides ... (-:

--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

"So, I take it you've ... been with a man before?" "I'm a virgin. I'm just not
very good at it." Topper Harley & Ramada Thompson (Charlie Sheen & Valeria
Golino), in "Hot Shots!" (1991).

[SpamTrapSeeSig]

In article <hs11l8leaoc1sn2r8...@4ax.com>, Java Jive
<ja...@evij.com.invalid> writes

>the top end of AC is limited
>by the slow tape speed to about 16kHz or so

It's inversely proportional to the replay head gap. Tape speed
theoretically doesn't have anything to do with it (until you get down to
1/2 wavelength ~ particle size), although it does affect the noise
characteristics.

The recording head gap doesn't matter much (within reason) as recording
happens as the tape leaves the head's field, not in the gap itself.

--
SimonM

[Java Jive]

I've forgotten now whatever hardware level theory I once knew, it's
all a jumble of bias frequency and tape hysteresis, but ...

On Thu, 28 Mar 2013 09:51:33 +0000, SpamTrapSeeSig
<no-...@nospam.virginmedia.net> wrote:

> In article <hs11l8leaoc1sn2r8...@4ax.com>, Java Jive
> <ja...@evij.com.invalid> writes
> >the top end of AC is limited
> >by the slow tape speed to about 16kHz or so
>
> It's inversely proportional to the replay head gap.

I remember gap width as being important as well. When I replaced a
set of worn heads on an old TC-330 the improvement in the top end was
noticeable.

> Tape speed
> theoretically doesn't have anything to do with it (until you get down to
> 1/2 wavelength ~ particle size), although it does affect the noise
> characteristics.

Whatever the theory, in practice I'm right about the tape-speed
determining the top cut-off point (and actually these figures are much
worse than I remembered them, wish I'd kept the manual when I threw
out the machine):
http://www.ebay.com/itm/Original-Factory-Sony-TC-330-Reel-Reel-Tape-Deck-Service-Manual-/111009807072?pt=Vintage_Electronics_R2&hash=item19d8b33ae0

Open-reel section
30Hz - 18KHz at 19cm/s
30Hz - 13kHz at 9.5cm/s
30Hz - 7kHz at 4.8cm/s

Audio-cassette section
50Hz - 10kHz

> The recording head gap doesn't matter much (within reason) as recording
> happens as the tape leaves the head's field, not in the gap itself.

My experience above of replacing knackered heads leads me to disagree
with this as well.

Cue Jim Lesurf?

[SpamTrapSeeSig]

In article <4i68l8571fu2sq796...@4ax.com>, Java Jive

<ja...@evij.com.invalid> writes
>I've forgotten now whatever hardware level theory I once knew, it's
>all a jumble of bias frequency and tape hysteresis, but ...
>
>On Thu, 28 Mar 2013 09:51:33 +0000, SpamTrapSeeSig
><no-...@nospam.virginmedia.net> wrote:
>
>> In article <hs11l8leaoc1sn2r8...@4ax.com>, Java Jive
>> <ja...@evij.com.invalid> writes
>> >the top end of AC is limited
>> >by the slow tape speed to about 16kHz or so
>>
>> It's inversely proportional to the replay head gap.
>
>I remember gap width as being important as well. When I replaced a
>set of worn heads on an old TC-330 the improvement in the top end was
>noticeable.

TC330s had notoriously soft material for the heads, and a very narrow
replay gap to increase the frequency response (I think there was a
_very_ pronounced dovetail shape to the gap, too. They didn't stay
fettled for very long as a consequence, and I always smile when I see
the occasional one come up on eBay.

I can't understand what punters think that type of thing is going to do
these days -- it's like the penchant for germanium transistor circuitry
in studios: "move on, nothing to see (or listen to) here." Someone was
recently trying to sell bits of a mono Longden desk for �13,000. I can't
deny that JL did a brilliant job creating them, but using it now?

As I get older I realise the world is far weirder than I could possibly
have imagined as a teenager.

S.


--
SimonM

[Clive]

In message <4i68l8571fu2sq796...@4ax.com>, Java Jive
<ja...@evij.com.invalid> writes

>Whatever the theory, in practice I'm right about the tape-speed
>determining the top cut-off point (and actually these figures are much
>worse than I remembered them, wish I'd kept the manual when I threw
>out the machine):

Indeed you are, it's a combination of tape head width and tape speed,
higher speed and smaller tape head gap mean better frequency response,
track width is the one that seriously affects noise, increasing by 3dB
for halving of the track width.
--
Clive

[Roderick Stewart]

On Thu, 28 Mar 2013 11:07:06 +0000, Clive <cl...@yewbank.demon.co.uk>
wrote:

>>Whatever the theory, in practice I'm right about the tape-speed
>>determining the top cut-off point (and actually these figures are much
>>worse than I remembered them, wish I'd kept the manual when I threw
>>out the machine):
>Indeed you are, it's a combination of tape head width and tape speed,
>higher speed and smaller tape head gap mean better frequency response,
>track width is the one that seriously affects noise, increasing by 3dB
>for halving of the track width.

And it can all be a waste of time if the HF bias and equalisation are
not correctly adjusted for the particular combination of machine and
tape. This was probably never done for most domestic recording
equipment once it left the factory, probably resulting in a lot of
false impressions of what magnetic tape was capable of.

Rod.

[John Williamson]

On 28/03/2013 10:49, Java Jive wrote:
> I've forgotten now whatever hardware level theory I once knew, it's
> all a jumble of bias frequency and tape hysteresis, but ...
>
> On Thu, 28 Mar 2013 09:51:33 +0000, SpamTrapSeeSig
> <no-...@nospam.virginmedia.net> wrote:
>
>> In article <hs11l8leaoc1sn2r8...@4ax.com>, Java Jive
>> <ja...@evij.com.invalid> writes
>>> the top end of AC is limited
>>> by the slow tape speed to about 16kHz or so
>>
>> It's inversely proportional to the replay head gap.
>
> I remember gap width as being important as well. When I replaced a
> set of worn heads on an old TC-330 the improvement in the top end was
> noticeable.
>

That's because as the head wears, the gap becomes wider and also loses
its straight edges. The effect is mich more noticeable on a head used
for playback than on a head used to record.

>> Tape speed
>> theoretically doesn't have anything to do with it (until you get down to
>> 1/2 wavelength ~ particle size), although it does affect the noise
>> characteristics.
>
> Whatever the theory, in practice I'm right about the tape-speed
> determining the top cut-off point (and actually these figures are much
> worse than I remembered them, wish I'd kept the manual when I threw
> out the machine):
> http://www.ebay.com/itm/Original-Factory-Sony-TC-330-Reel-Reel-Tape-Deck-Service-Manual-/111009807072?pt=Vintage_Electronics_R2&hash=item19d8b33ae0
>
> Open-reel section
> 30Hz - 18KHz at 19cm/s
> 30Hz - 13kHz at 9.5cm/s
> 30Hz - 7kHz at 4.8cm/s
>
> Audio-cassette section
> 50Hz - 10kHz
>

All about average for the period, limited by both the playback EQ curves
as laid down in the standards and the width of the gap in the playback head.

>> The recording head gap doesn't matter much (within reason) as recording
>> happens as the tape leaves the head's field, not in the gap itself.
>
> My experience above of replacing knackered heads leads me to disagree
> with this as well.
>

The most important thing about the recording head is the straightness of
the trailing gap edge. I used to own an Akai X-IV portable with a
seperate bias head that would play back the bias tone from the
crossfield head at audible frequencies if you reduced the tape speed enough.

It used the same head for recording and playback, so would have been
capable of recording frequencies of more than 20KHz at 7 1/2 ips if the
electronics had let it. I really regret letting that recorder go.

[Java Jive]

On Thu, 28 Mar 2013 17:02:12 +0000, John Williamson
<johnwil...@btinternet.com> wrote:

> On 28/03/2013 10:49, Java Jive wrote:
> >
> > I remember gap width as being important as well. When I replaced a
> > set of worn heads on an old TC-330 the improvement in the top end was
> > noticeable.
> >
> That's because as the head wears, the gap becomes wider and also loses
> its straight edges. The effect is mich more noticeable on a head used
> for playback than on a head used to record.

Exactly.

> All about average for the period, limited by both the playback EQ curves
> as laid down in the standards and the width of the gap in the playback head.

Maybe, but for some reason I remembered them as being better.

This sort of knowledge has come rather back into prominence recently
with the recent misguided myths that somehow old audio technology was
better. A few years ago, the absurdity of these myths led me to
research a page for my site debunking analogue recording technology,
and I think I may subsequently have confused some of my TC-330 specs
with best of breed, which it definitely wasn't.

> The most important thing about the recording head is the straightness of
> the trailing gap edge. I used to own an Akai X-IV portable with a
> seperate bias head that would play back the bias tone from the
> crossfield head at audible frequencies if you reduced the tape speed enough.
>
> It used the same head for recording and playback, so would have been
> capable of recording frequencies of more than 20KHz at 7 1/2 ips if the
> electronics had let it. I really regret letting that recorder go.

That's rather unexpected. As I've already admitted, my memory of this
stuff is getting hazy, but ISTR that the bias couldn't be recorded.

Let's do some work ...

From the specs above, the bias was 85kHz, so at 19cm/s, each
wavelength of bias was 0.19 / 85000 = 2.2 m-6, so, according to
information theory, the size of field to be discriminated would have
to be half that, or 1.1 microns.

http://en.wikipedia.org/wiki/Magnetic_storage#Analog_recording

"The commonly used magnetic particles are Iron oxide particles or
Chromium oxide and metal particles with size of 0.5 micrometers."

So that's ok. Now head gap width ...

http://en.wikipedia.org/wiki/Tape_head

"The desirability for a narrow gap means that most practical heads are
made by forming a narrow V-shaped groove in the back face of the core,
and grinding away the front face until the V-groove is just breached.
In this way, gaps of the order of micrometres are achievable."

Note micrometres in the plural. Your claim sounds unlikely to me. Are
you sure it was the bias you were hearing?

[John Williamson]

On 28/03/2013 23:03, Java Jive wrote:

> Note micrometres in the plural. Your claim sounds unlikely to me. Are
> you sure it was the bias you were hearing?
>

Yes. I recorded originally at 7 1/2 ips, then played back at 15/16 ips.
The recording was made with no input, as I was trying to work out what
the whistle was.

[J. P. Gilliver (John)]

In message <QXulqmNl...@virginmedia.net>, SpamTrapSeeSig

<no-...@nospam.virginmedia.net> writes:
>In article <hs11l8leaoc1sn2r8...@4ax.com>, Java Jive
><ja...@evij.com.invalid> writes
>>the top end of AC is limited
>>by the slow tape speed to about 16kHz or so
>
>It's inversely proportional to the replay head gap. Tape speed

I don't think that's _completely_ true - see below.

>theoretically doesn't have anything to do with it (until you get down
>to 1/2 wavelength ~ particle size), although it does affect the noise
>characteristics.

Agreed.

>
>The recording head gap doesn't matter much (within reason) as recording
>happens as the tape leaves the head's field, not in the gap itself.
>

I have the feeling that there will be _some_ pickup of signals whose
wavelength is much less than the replay head gap - just you'll get
strange aliasing-like nulls in the frequency _response_. Say, for
example, there are three half-wavelengths across the gap, then I think
you'd get the same amount of output as from a gap one half-wavelength
wide. On the way up to that frequency, though, you'd pass through a
frequency where the gap (well, allowing for edge effects and other such
field anomalies) was exactly one wavelength, at which I think you'd get
no output.

I think it's like aerials: a three-half-wavelegnth one will give the
same output as a one-half-wavelength one; since it uses three times as
much metal and takes up three times the space, there's no advantage to
it. It's the _difference_ between the ends that matters.

I always think of this analogy - don't know if it will help anyone: I
think of an aerial as like a bar with floats on the end, extracting
energy from water waves coming at it end on, but the output is from
something fixed to its midpoint, and only _torsional_ energy can be
extracted. So when waves come along that have a wavelength twice that of
the bar, i. e. the rod is half a wavelength, the opposite ends of the
bar will go up and down with maximum difference, so the rod fixed to the
midpoint (through which you're extracting signal) will twist by the
maximum. If waves of half the wavelength come along (wavelength _same
as_ the bar), both ends of the bar will go up and down together, so the
rod fixed to the midpoint - though it will be flapping up and down a lot
- won't _twist_ at all. Other wavelengths will have other effects: very
long ones, for example (however big), will move both ends of the bar up
and down almost together, so very little twisting output will be
obtained. Very short ones will give some twisting, if the bar isn't an
exact multiple of their wavelength, but not nearly as much as a shorter
bar would.

--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

What a strange illusion it is to suppose that beauty is goodness. -Leo Tolstoy,
novelist and philosopher (1828-1910)

[Jim Lesurf]

In article <4i68l8571fu2sq796...@4ax.com>, Java Jive

<ja...@evij.com.invalid> wrote:
> I've forgotten now whatever hardware level theory I once knew, it's all
> a jumble of bias frequency and tape hysteresis, but ...

> On Thu, 28 Mar 2013 09:51:33 +0000, SpamTrapSeeSig
> <no-...@nospam.virginmedia.net> wrote:

> >
> > It's inversely proportional to the replay head gap.

> I remember gap width as being important as well. When I replaced a set
> of worn heads on an old TC-330 the improvement in the top end was
> noticeable.

As ever, its more complex than just one factor, as the discussion has
already shown.

The Tandberg decks I've used all employ a 'cross field' head to allow the
recording head to work better. And the replay head can have a smaller
effective gap. The recording head can record shorter wavelengths than its
gap might imply because the remaining imposed magnetisation is set by the
'trailing edge' of the apllied fields.

> > Tape speed theoretically doesn't have anything to do with it (until
> > you get down to 1/2 wavelength ~ particle size), although it does
> > affect the noise characteristics.

> Whatever the theory, in practice I'm right about the tape-speed
> determining the top cut-off point (and actually these figures are much
> worse than I remembered them, wish I'd kept the manual when I threw out
> the machine):
> http://www.ebay.com/itm/Original-Factory-Sony-TC-330-Reel-Reel-Tape-Deck-Service-Manual-/111009807072?pt=Vintage_Electronics_R2&hash=item19d8b33ae0

> Open-reel section 30Hz - 18KHz at 19cm/s 30Hz - 13kHz at 9.5cm/s 30Hz -
> 7kHz at 4.8cm/s

As below, various reel decks could fo better than that. Although how much
it mattered for home recording is questionable in an age when home
equipment probably didn't give much useful around 18kHz upwards! I suspect
most people used the nicer 'hifi' tape decks to record from the radio or
their friend's LPs. FM radio means you don't want > 16 kHz. Most LPs and
cartridges wouldn't have produced much that was useful by 20kHz.

> Audio-cassette section 50Hz - 10kHz

A number of cassette deck designs could do rather better than that. Naks,
Revox, etc. They easily provided a pretty flat response to 20kHz. ...at a
cost, of course. :-)

> > The recording head gap doesn't matter much (within reason) as
> > recording happens as the tape leaves the head's field, not in the gap
> > itself.

> My experience above of replacing knackered heads leads me to disagree
> with this as well.

> Cue Jim Lesurf?

As usual: Devil in all the details. The 'hard' heads developed later on in
the life of analogue tape both resisted wear and allowed for smaller gaps.
Also higher field levels. Ealier designs wore down, particularly if used
with tapes that were more abrasive. So measured well in a review, but
deteriorated swiftly in use.

FWIW I still have a Nak C2 that works nicely. But I only use it to play old
tapes to transfer to digital. I'd be doing the same for reel to reel. But
I've not yet sorted out the problems with my ancient Tandbergs.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
Audio Misc http://www.audiomisc.co.uk/index.html
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html

[SpamTrapSeeSig]

In article <arjbcn...@mid.individual.net>, John Williamson
<johnwil...@btinternet.com> writes

>> Open-reel section
>> 30Hz - 18KHz at 19cm/s
>> 30Hz - 13kHz at 9.5cm/s
>> 30Hz - 7kHz at 4.8cm/s
>>
>> Audio-cassette section
>> 50Hz - 10kHz
>>
>All about average for the period, limited by both the playback EQ
>curves as laid down in the standards and the width of the gap in the
>playback head.
>
>>> The recording head gap doesn't matter much (within reason) as recording
>>> happens as the tape leaves the head's field, not in the gap itself.
>>
>> My experience above of replacing knackered heads leads me to disagree
>> with this as well.
>>
>The most important thing about the recording head is the straightness
>of the trailing gap edge. I used to own an Akai X-IV portable with a
>seperate bias head that would play back the bias tone from the
>crossfield head at audible frequencies if you reduced the tape speed
>enough.

Nagras 4-series could do that too, although obviously not crossfield
bias. Their bias frequency was quite low - somewhere in the 30-40kHx
range, IIRC. I never noticed the same thing with Studers, and assumed
their bias was higher frequency. I think it was chosen to match the head
design rather than the stock, but I'll be digging Jorgensen out at this
rate ;-)

--
SimonM

[SpamTrapSeeSig]

In article <i1g9l8hrqv10vm6m1...@4ax.com>, Java Jive
<ja...@evij.com.invalid> writes

>On Thu, 28 Mar 2013 17:02:12 +0000, John Williamson
><johnwil...@btinternet.com> wrote:
>
>> On 28/03/2013 10:49, Java Jive wrote:
>> >
>> > I remember gap width as being important as well. When I replaced a
>> > set of worn heads on an old TC-330 the improvement in the top end was
>> > noticeable.
>> >
>> That's because as the head wears, the gap becomes wider and also loses
>> its straight edges. The effect is mich more noticeable on a head used
>> for playback than on a head used to record.
>
>Exactly.
>
>> All about average for the period, limited by both the playback EQ curves
>> as laid down in the standards and the width of the gap in the playback head.
>
>Maybe, but for some reason I remembered them as being better.
>
>This sort of knowledge has come rather back into prominence recently
>with the recent misguided myths that somehow old audio technology was
>better. A few years ago, the absurdity of these myths led me to
>research a page for my site debunking analogue recording technology,
>and I think I may subsequently have confused some of my TC-330 specs
>with best of breed, which it definitely wasn't.

Too right. the Akai 4000 series and the TC330s were very popular and
equally horrible. IIRC the Akais had worse wow and flutter, but there
wasn't much else in it. You changed speed on the 4000 by use of a sleeve
over the capstan with a locknut (and an eq switch).

>"The desirability for a narrow gap means that most practical heads are
>made by forming a narrow V-shaped groove in the back face of the core,
>and grinding away the front face until the V-groove is just breached.
>In this way, gaps of the order of micrometres are achievable."
>
>Note micrometres in the plural. Your claim sounds unlikely to me. Are
>you sure it was the bias you were hearing?

It was bias, most probably.

And the Wikipedia article is a bit erroneous. You can't consider
recording and replay functions in the same way - combined function heads
were always a nasty compromise.

The reason for the rear cutaway angle in recording heads is to help
direct the flux out of the side of the pole pieces into the medium. I
think paramagnetic inserts were also used (can't remember what, though).

As I said, recording takes place as the medium leaves the influence of
the recording head, not across the pole pieces. The sharper you can make
the magnetic transition, the better the frequency response. The function
of the gap it to get the right shaped field (in 2D, perpendicular to the
tape axis), its width isn't significant, although as discussed, if the
trailing edge is ragged it will cause HF self-erasure. Assuming in all
cases the head is on-azimuth, etc.

In the case of replay, it's simpler: the narrower the gap the higher the
reproducible frequency, for a given tape speed. That's why you get the
characteristic response 'bumps' that trail off above the upper linear
limit. If 3 lambda fits in the gap, for example, you get significant
output.
--
SimonM

[Jim Lesurf]

In article <DuQwW7hr...@soft255.demon.co.uk>, J. P. Gilliver (John)

<G6...@soft255.demon.co.uk> wrote:

> >
> >The recording head gap doesn't matter much (within reason) as recording
> > happens as the tape leaves the head's field, not in the gap itself.
> >
> I have the feeling that there will be _some_ pickup of signals whose
> wavelength is much less than the replay head gap - just you'll get
> strange aliasing-like nulls in the frequency _response_. Say, for
> example, there are three half-wavelengths across the gap,

Yes. The replay side of this is a classic 'convolution problem' in physics
and maths terms. It is complicated because the sensor (head and gap) don't
have a sensitivity pattern that is rectangular. For the same reason you
also get low frequency wiggles in the response determined by factors like
the overall head size, shape, etc.

The recording side is rather different as the 'trailing edge' of the field
being applied tends to 'wipe' what other parts previously imposed. Hence
the angled offset 'cross field' recording systems can have a smaller and
more controlled effective gap.

[SpamTrapSeeSig]

In article <5334010...@audiomisc.co.uk>, Jim Lesurf
<no...@audiomisc.co.uk> writes

>In article <DuQwW7hr...@soft255.demon.co.uk>, J. P. Gilliver (John)
><G6...@soft255.demon.co.uk> wrote:
>
>> >
>> >The recording head gap doesn't matter much (within reason) as recording
>> > happens as the tape leaves the head's field, not in the gap itself.
>> >
>> I have the feeling that there will be _some_ pickup of signals whose
>> wavelength is much less than the replay head gap - just you'll get
>> strange aliasing-like nulls in the frequency _response_. Say, for
>> example, there are three half-wavelengths across the gap,
>
>Yes. The replay side of this is a classic 'convolution problem' in physics
>and maths terms. It is complicated because the sensor (head and gap) don't
>have a sensitivity pattern that is rectangular. For the same reason you
>also get low frequency wiggles in the response determined by factors like
>the overall head size, shape, etc.
>
>The recording side is rather different as the 'trailing edge' of the field
>being applied tends to 'wipe' what other parts previously imposed. Hence
>the angled offset 'cross field' recording systems can have a smaller and
>more controlled effective gap.

Quite so. The other advantage of crossfield bias was that you could
optimise the bias head for the single higher frequency it operated at,
and the record head didn't need to work up to the bias frequency either.

All this of course was offset against the significant increase in
mechanical complexity, and operational issues like splicing tape
upsetting things.

--
SimonM

[Clive]

In message <m7OohSdm...@virginmedia.net>, SpamTrapSeeSig
<no-...@nospam.virginmedia.net> writes

>the Akai 4000 series and the TC330s were very popular

Didn't the Akai 330 take 10 1/2 inch spools and a cross field head?
--
Clive

[Clive]

In message <rbbr5zcw...@virginmedia.net>, SpamTrapSeeSig
<no-...@nospam.virginmedia.net> writes

>Nagras 4-series could do that too, although obviously not crossfield
>bias. Their bias frequency was quite low - somewhere in the 30-40kHx
>range, IIRC. I never noticed the same thing with Studers, and assumed
>their bias was higher frequency. I think it was chosen to match the
>head design rather than the stock, but I'll be digging Jorgensen out at
>this rate ;-)

I have a Revox A77 which was made by Studer and whilst the standard bias
frequency of the time was 90kHz, the Revox has an Erase and Bias
frequencies of 120kHz.
--
Clive

[Clive]

In message <5333f64...@audiomisc.co.uk>, Jim Lesurf
<no...@audiomisc.co.uk> writes

>Ealier designs wore down, particularly if used
>with tapes that were more abrasive. So measured well in a review, but
>deteriorated swiftly in use.

Correct, mu-metal heads had a life expectance of 500 hours.
--
Clive

[Mark Carver]

hwh wrote:

> My uncle was offered a 'color aerial' decades back. And yes, we
> continentals had color on VHF ;-)

Well, we Brits put the U in colour, and the frequency ;-)

--
Mark
Please replace invalid and invalid with gmx and net to reply.

www.paras.org.uk

[Clive]

In message <5334010...@audiomisc.co.uk>, Jim Lesurf
<no...@audiomisc.co.uk> writes

>The recording side is rather different as the 'trailing edge' of the field
>being applied tends to 'wipe' what other parts previously imposed. Hence
>the angled offset 'cross field' recording systems can have a smaller and
>more controlled effective gap.

As I remember it, audio will not leave an imprint on the tape because of
the hysteresis which is needed to keep the recorded item on the tape.
A high frequency waveform is applied to the tape very much the same as a
Carrier wave carries signal from one place to another , the only
difference being that the carrier is modulated in an A.M. Radio, whereas
bias is used to "punch" the signal into the tape pass the hysteresis
boundary and is at a constant level set by the characteristics of the
tape.
What you've written looks to be a straight steal from Wonkipedia and is
wrong.
--
Clive

[Clive]

In message <3LWdnU_ETo8lV8jM...@brightview.co.uk>, Mark
Carver <mark....@invalid.invalid> writes

>hwh wrote:
>> My uncle was offered a 'color aerial' decades back. And yes, we
>> continentals had color on VHF ;-)
>Well, we Brits put the U in colour, and the frequency ;-)

In fact our first colour broadcast was on 10/10/1955 after the close of
service from Alexandria Palace in N.T.S.C. (Never Twice the Same
Colour).
It wasn't adopted because of the colour distortion caused by attenuation
of the sidebands in the sub-carrier. Phase Alternating Line was known
about as it was supposed to correct the errors by eye, but instead made
a nasty crawling dot pattern known as Hanover Blind and can be seen in
Simple PAL sets. PAL came into it's own when Telefunken perfected the
sum and difference effects of PAL using a glass delay line, with the
outcome that in the face of serious disorder in the signal, instead of
Hanover Blind all that happened was desaturation of the hue signal
presented to the CRT.
--
Clive

[Max Demian]

"Clive" <cl...@yewbank.demon.co.uk> wrote in message
news:LmuEOCIu...@yewbank.demon.co.uk...

In the early days of domestic tape recorders the heads could be unplugged
and replaced.

--
Max Demian

[hwh]

On 3/29/13 6:09 PM, Mark Carver wrote:
> hwh wrote:
>
>> My uncle was offered a 'color aerial' decades back. And yes, we
>> continentals had color on VHF ;-)
>
> Well, we Brits put the U in colour, and the frequency ;-)

Oops. Oh well. Don't start about elevators. Or aerials ;)

gr, hwh

[Java Jive]

On Fri, 29 Mar 2013 17:21:20 +0000, Clive <cl...@yewbank.demon.co.uk>
wrote:

<
> As I remember it, audio will not leave an imprint on the tape because of
> the hysteresis which is needed to keep the recorded item on the tape.

Yes, this is something I do vaguely remember ...

> A high frequency waveform is applied to the tape very much the same as a
> Carrier wave carries signal from one place to another , the only
> difference being that the carrier is modulated in an A.M. Radio, whereas
> bias is used to "punch" the signal into the tape pass the hysteresis
> boundary and is at a constant level set by the characteristics of the
> tape.

Yes, the purpose of the 'carrier wave' bias was so that the recordings
could be made at magnetic intensity (IIRC?) levels where the
hysteresis characteristic of the recording tape was at its most linear
= less distortion in the played back result.

[J. P. Gilliver (John)]

In message <iX6eC7L9...@yewbank.demon.co.uk>, Clive

I don't think Hanover blind was a _dot_ crawl pattern as such, more a
pairing of lines with opposite colour errors.

--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

Have you ever tried Chicken Tarka? It's like Chicken Tikka, only 'otter.

[charles]

In article <LbfirgQU...@soft255.demon.co.uk>,

J. P. Gilliver (John) <G6...@soft255.demon.co.uk> wrote:

> In message <iX6eC7L9...@yewbank.demon.co.uk>, Clive
> <cl...@yewbank.demon.co.uk> writes:
> >In message <3LWdnU_ETo8lV8jM...@brightview.co.uk>, Mark
> >Carver <mark....@invalid.invalid> writes
> >>hwh wrote:
> >>> My uncle was offered a 'color aerial' decades back. And yes, we
> >>> continentals had color on VHF ;-)
> >>Well, we Brits put the U in colour, and the frequency ;-)
> >In fact our first colour broadcast was on 10/10/1955 after the close of
> >service from Alexandria Palace in N.T.S.C. (Never Twice the Same
> >Colour).
> >It wasn't adopted because of the colour distortion caused by
> >attenuation of the sidebands in the sub-carrier. Phase Alternating
> >Line was known about as it was supposed to correct the errors by eye,
> >but instead made a nasty crawling dot pattern known as Hanover Blind
> >and can be seen in Simple PAL sets. PAL came into it's own when
> >Telefunken perfected the sum and difference effects of PAL using a
> >glass delay line, with the outcome that in the face of serious disorder
> >in the signal, instead of Hanover Blind all that happened was
> >desaturation of the hue signal presented to the CRT.

> I don't think Hanover blind was a _dot_ crawl pattern as such, more a
> pairing of lines with opposite colour errors.

and usually known as "Hanover Bars"

--
From KT24

Using a RISC OS computer running v5.18

[Curtis Interruptus]

On Mar 29, 5:38 pm, Clive <cl...@yewbank.demon.co.uk> wrote:
> In message <3LWdnU_ETo8lV8jMnZ2dnUVZ8oudn...@brightview.co.uk>, Mark

I get the impression that you think that you understand PAL (and by
definition NTSC), so I'll keep it simple for you

Hanover lines are caused, in simple PAL, by a phase shift on alternate
lines leading a "venetian blind" effect on the image. Alternate lines,
when a phase error is present, swing alternately towards the red and
blue axes (as seen on a vectorscope), a delay line system will
effectively add the errors and display the difference between the two
(but given the way that the summation takes place, the saturation will
decrease at the cost of displaying the correct chroma phase).

The dot patterning to which I assume that you refer, is caused when
there is a fixed mathematical relationship between the CSC and line
frequencies. (283.75 in the original 625/50 PAL). Older readers may
know this frequency as (F)nat. The precision offset of 25Hz was added
resulting in (F)csc. The septics got round the same issue by changing
the Frame rate by 1% (hence 525/59.940.

[SpamTrapSeeSig]

In article <FGBH2pKQ...@yewbank.demon.co.uk>, Clive
<cl...@yewbank.demon.co.uk> writes

I don't know where you got that lot from, but Jim's quite correct.

Bias is to make the transfer characteristic as linear as possible, and
I'm fairly certain machines without bias were used in the early days of
magnetic recording. They worked, just not very well. I think Marconi
Stille machines didn't use bias, but I may be wrong about that.

Hysteresis is a physical property of the recording medium, not something
you do to it.


--
SimonM

[charles]

In article
<723cf671-f0b2-4f00...@l9g2000yqp.googlegroups.com>,

they also had a problem with interference from the sound carrier which was
the main reason for the 1% change in frame rate. But, it's nearly 50 years
since I knew the maths.

[Clive]

In message <53342811...@charleshope.demon.co.uk>, charles
<cha...@charleshope.demon.co.uk> writes

>and usually known as "Hanover Bars"

Perhaps it's known as different names depending on where you were when
learning, these names tend to stick.
--
Clive

[Clive]

In message <sjsqHehv...@virginmedia.net>, SpamTrapSeeSig
<no-...@nospam.virginmedia.net> writes

I agree with your last sentence, hysteresis is a property of the
magnetic medium, without it as soon as you removed the polarising field,
the field in the medium would go as well. The bias does exactly the
same to cold tape as heat does when copying at high speed and a high
temperature when it exceeds it's Curie point only whilst copying and
dropping below it to retain the magnetic image. I can remember a tape
recorder that had a DC magnet as the bias, it was appalling.
--
Clive

[charles]

In article <ij4ev$S2UfV...@yewbank.demon.co.uk>,

you mentioned Fnat, so I assume you learned things at the BBC. I don't
think anyone else used it - or even knew what it was.

[Johny B Good]

Originally, an actual DC bias was used to overcome the hysteresis
effect which caused a form of distortion analogous to that exhibited
by a sticking loudspeaker voice coil[1] where signals below a certain
threshold would fail to record (just as very quiet levels would fail
to be reproduced by a loudspeaker suffering a sticking voice coil)
with higher levels producing a very gritty sounding distorted parody
and very loud levels producing an almost distortionless recording due
to the much stronger recording masking out the effects of the
distortion.

This worked but at the cost of increased noise and reduced dynamic
range. The noise increase was the result of two seperate mechanisms.
The first being simply due to turning a random collection of magnetic
particles into a random collection of magnets. The second being down
to scrape modulation now having a permanently magnetised source to
work with.

Although erase typically took the form of a swingaway permanent
magnet to remagnetise to saturation in the opposite sense to the DC
bias, you still had to avoid reversals of magnetic flux by the
combined effects of the DC bias and recording signal, effectively
halving the amplitude range that was potentially available.

Ultrasonic AC bias and erase, provided the solution to all of the
above shortcomings. Although an AC signal approximately ten times the
maximum recording signal level isn't normally regarded as being a bias
of any sort in any other system, the name stuck by virtue of its
original function in magnetic recorders and an absence of a ready to
hand substitute word to replace it.

The only concession to the use of ultrasonic AC instead of DC being
the addition of the AC suffix to distinguish it from its precursor.
Nowadays, hearking back to the 60s, any references to tape recording
bias are made on the assumption that the original DC bias technique
has long since been obsoleted by the use of AC bias and the AC suffix
is generally discarded as being superfluous. The assumption being that
any mention of bias is a reference to AC bias unless, exceptionally,
ancient recording machines are being discussed when it is assumed the
DC prefix will be applied to avoid any confusion.


[1] Alternatively the other analogy commonly used was that it was akin
to the 'crossover distortion' that would ensue in a class B amplifier
lacking the necessary bias required to avoid the 'dead zone'.
--
Regards, J B Good

[Clive]

In message
<723cf671-f0b2-4f00...@l9g2000yqp.googlegroups.com>,
Curtis Interruptus <curtisth...@gmail.com> writes

>I get the impression that you think that you understand PAL (and by
>definition NTSC), so I'll keep it simple for you

Thank you

>Hanover lines are caused, in simple PAL, by a phase shift on alternate
>lines leading a "venetian blind" effect on the image

The phase shift occurs to the chroma signal, (two in quadrature, giving
one resultant sub-carrier) whose phase is concurrent with the desired
colour has rotated about it's axis because of sideband attenuation in
either or both of the two colour difference signals. So where in NTSC
you'd get a colour shift that you can partially correct with a hue
control, in simple PAL you would get a two line structure (each line
being either side of the required colour giving narrow lines (bars if
you like) crawling up the screen .

> Alternate lines,
>when a phase error is present, swing alternately towards the red and
>blue axes (as seen on a vectorscope), a delay line system will
>effectively add the errors and display the difference between the two
>(but given the way that the summation takes place, the saturation will
>decrease at the cost of displaying the correct chroma phase).
>
>The dot patterning to which I assume that you refer, is caused when
>there is a fixed mathematical relationship between the CSC and line
>frequencies. (283.75 in the original 625/50 PAL). Older readers may
>know this frequency as (F)nat. The precision offset of 25Hz was added
>resulting in (F)csc. The septics got round the same issue by changing
>the Frame rate by 1% (hence 525/59.940.

The dot structure to which I refer can be seen at it's clearest on
colour bars between Magenta and Green stripes.
Thank you again for keeping it simple for me.
--
Clive

[Clive]

In message <g1tbl8tigloeq58a3...@4ax.com>, Johny B Good
<johnny...@invalid.ntlworld.com> writes

>[1] Alternatively the other analogy commonly used was that it was akin
>to the 'crossover distortion' that would ensue in a class B amplifier
>lacking the necessary bias required to avoid the 'dead zone'.

Indeed, your reference to a class B amplifier is very apt, but I would
change crossover distortion which implies insufficient transistor base
bias to the output pair, to no base bias giving only the peaks positive
and negative and a flat or null signal crossover region, the harmonics
of which are dire.
--
Clive

[Clive]

In message <53342ffc...@charleshope.demon.co.uk>, charles
<cha...@charleshope.demon.co.uk> writes

>you mentioned Fnat, so I assume you learned things at the BBC. I don't
>think anyone else used it - or even knew what it was.

I'm sorry, but you've wrongly attributed this to me.
--
Clive

[Ian Jackson]

In message <T9nyYYVI...@yewbank.demon.co.uk>, Clive
<cl...@yewbank.demon.co.uk> writes

With no DC bias, class B push-pull audio amplifiers have dire distortion
at small signals levels. The % distortion decreases as the signal level
is increased (as the waveform spends most of its time in the linear
region).

The distortion of a low-level signal (on one frequency) decreases when a
second signal (on a different frequency) is added (particularly if it
has a higher level) as this keeps the low-level signal in the linear
region for most of the time. In this respect, the effect is somewhat
similar to that of using AC bias for a record head.
--
Ian

[Clive]

In message <rmFfC4LN...@g3ohx.demon.co.uk>, Ian Jackson
<ianREMOVET...@g3ohx.demon.co.uk> writes

>With no DC bias, class B push-pull audio amplifiers have dire
>distortion at small signals levels. The % distortion decreases as the
>signal level is increased (as the waveform spends most of its time in
>the linear region).
>
>The distortion of a low-level signal (on one frequency) decreases when
>a second signal (on a different frequency) is added (particularly if it
>has a higher level) as this keeps the low-level signal in the linear
>region for most of the time. In this respect, the effect is somewhat
>similar to that of using AC bias for a record head.

I agree.
--
Clive

[Max Demian]

"Johny B Good" <johnny...@invalid.ntlworld.com> wrote in message
news:g1tbl8tigloeq58a3...@4ax.com...

Reminds me of my old Grundig Cub recorder, with spool drive, DC bias and
permanent magnet erase, which worked surprisingly well, for speech at any
rate. I think that there were some really cheap cassette recorders that used
DC bias and erase.

--
Max Demian

[Jim Lesurf]

In article <FGBH2pKQ...@yewbank.demon.co.uk>, Clive

What you missed is that the field I was referring to is the combination of
the audio waveform and the bias. :-) Hence the conclusions you jump to are
false.

It is also rather more complex than you state. Audio alone would leave some
recorded magnetisation patterns. But they would be severely distorted
because the magnetisation curves are so nonlinear and have hysteresis. And
the degree of penetation varies with frequency as well as level.

FWIW some advocates have developed analogue audio tape recording with no
bias oscillation. But it is very hard to make that work well, so using bias
makes more sense in practice.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
Audio Misc http://www.audiomisc.co.uk/index.html
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html

[Jim Lesurf]

In article <rjnbl81u09idadsvo...@4ax.com>, Java Jive

<ja...@evij.com.invalid> wrote:
> On Fri, 29 Mar 2013 17:21:20 +0000, Clive <cl...@yewbank.demon.co.uk>
> wrote: <


> > A high frequency waveform is applied to the tape very much the same as
> > a Carrier wave carries signal from one place to another , the only
> > difference being that the carrier is modulated in an A.M. Radio,
> > whereas bias is used to "punch" the signal into the tape pass the
> > hysteresis boundary and is at a constant level set by the
> > characteristics of the tape.

> Yes, the purpose of the 'carrier wave' bias was so that the recordings
> could be made at magnetic intensity (IIRC?) levels where the hysteresis
> characteristic of the recording tape was at its most linear = less
> distortion in the played back result.

At the magnetic domain level analogue tape recording is more 'digital' than
people may realise. The applied field experienced by each domain is the
combination of the fields form nearby domains and the externally induced
field. Each individual domain can then flip state along its preferred axis,
altering what its neighbours experience. In this sense ultrasonic bias is
more akin to 'dither' in the effect it causes. There were some articles in
the early HFN about this some years ago. I think there were also some in
the JAES but I'd have to check.

The problem most people are familiar with is hysteresis. But the other
problem is that low fields tend not to manage to get many domains to flip
state because of the quantisation energy required. The bias allows this to
be 'randomised' to get a more linear response. In part this is because the
bias and signal fields are *not* uniform across the whole part of the tape
'being recorded'.

One of the points of the seperate cross-field bias head was to manipulate
the shape of the region subject to the combined fields and get better
results. (Another was to get away from saturation of the heads by not
having to put both bias and signal into the same head.)

[Jim Lesurf]

In article <g1tbl8tigloeq58a3...@4ax.com>, Johny B Good

<johnny...@invalid.ntlworld.com> wrote:


> [1] Alternatively the other analogy commonly used was that it was akin
> to the 'crossover distortion' that would ensue in a class B amplifier
> lacking the necessary bias required to avoid the 'dead zone'.

That's an interesting analogy as *Perfect* class-B would not give any
crossover distortion as described by theory. But reality tends to defeat
this hope once you go beyond any kind of lab demo that is tweaked with
insane levels of care and attention. :-)

[Jim Lesurf]

In article <sjsqHehv...@virginmedia.net>, SpamTrapSeeSig

I can't recall if the Blattnerphone or wire recorders used AC bias. But
over the history of magnetic recording people have repeatedly tried not
using any AC bias. They can generally get it to work on a lab bench. But in
practice is it like trying to balance a pencil on its tip to make it work
well! Any slight variations in the magnetic material, etc, upset the
results.

[Roger Wilmut]

In article <nITY9NeR...@virginmedia.net>,
SpamTrapSeeSig <no-...@nospam.virginmedia.net> wrote:

> In article <5334010...@audiomisc.co.uk>, Jim Lesurf
> <no...@audiomisc.co.uk> writes
> >In article <DuQwW7hr...@soft255.demon.co.uk>, J. P. Gilliver (John)
> ><G6...@soft255.demon.co.uk> wrote:
> >
> >> >
> >> >The recording head gap doesn't matter much (within reason) as recording
> >> > happens as the tape leaves the head's field, not in the gap itself.
> >> >
> >> I have the feeling that there will be _some_ pickup of signals whose
> >> wavelength is much less than the replay head gap - just you'll get
> >> strange aliasing-like nulls in the frequency _response_. Say, for
> >> example, there are three half-wavelengths across the gap,
> >
> >Yes. The replay side of this is a classic 'convolution problem' in physics
> >and maths terms. It is complicated because the sensor (head and gap) don't
> >have a sensitivity pattern that is rectangular. For the same reason you
> >also get low frequency wiggles in the response determined by factors like
> >the overall head size, shape, etc.

> >
> >The recording side is rather different as the 'trailing edge' of the field
> >being applied tends to 'wipe' what other parts previously imposed. Hence
> >the angled offset 'cross field' recording systems can have a smaller and
> >more controlled effective gap.
>

> Quite so. The other advantage of crossfield bias was that you could
> optimise the bias head for the single higher frequency it operated at,
> and the record head didn't need to work up to the bias frequency either.
>
> All this of course was offset against the significant increase in
> mechanical complexity, and operational issues like splicing tape
> upsetting things.

The problem with cross-field bias, which is a nice idea under ideal
conditions, arises when there is a build up of oxide on the head or
something which lifts the tape away from the head like a joint.

With conventional bias, this results in a reduction of bias level which
to some extent increases the hf response of the recording (at the
expense of noise and distortion) and so partially compensates for the
issue. With cross-filed bias, since these issues move the tape closer to
the bias head at the back of the tape, the bias level is increased,
which reduces the top and so makes matters worse.

[Roderick Stewart]

On Fri, 29 Mar 2013 20:08:33 +0000, Clive <cl...@yewbank.demon.co.uk>
wrote:

>I can remember a tape
>recorder that had a DC magnet as the bias, it was appalling.

So can I. At least you had to thread the tape differently for
recording, so that it would go past the magnet, and remember to
re-thread it for spooling and playback otherwise you'd erase the
recording, so I suppose that's what it was doing. It was a contraption
called the "Gramdeck" that just had the essentials of a tape recorder
which you'd place on a gramophone turntable to provide the constant
speed drive. It only produced recordings that corresponded to any
standardised tape speed (7.5 inch/sec) when the turntable was rotating
at 78rpm. Google, and be amazed.

Rod.

[Johny B Good]

A very good description.

>One of the points of the seperate cross-field bias head was to manipulate
>the shape of the region subject to the combined fields and get better
>results. (Another was to get away from saturation of the heads by not
>having to put both bias and signal into the same head.)
>

In the early days, the "Rule Of Thumb" concerning where to calibrate
the replay reference level was to set 0db VU at -12db saturation
level. Later, this replay level was referenced to an absolute flux
strength resulting in higher coercivity high output coatings raising
the saturation levels by more than this +12db margin.

Since the bias has to be able to saturate the tape, the bias current,
level would typically be set to around 7 to 10 times the 0dbVu mark
(which, if my recollection of it being 7 to 10 times the current,
would make it +13 to +20db stronger than the 0dbVU level). This is
stuff I was reading about over 4 decades ago so my recollection is a
little hazy on this point.

Whatever the case, using a seperate bias head would certainly reduce
the risk of saturation in the recording head pole tip material but
this wasn't the only reason for using crossfield bias. It was known
that the longer wavelengths penetrated the magnetic layer more deeply
than the shorter wavelengths which meant they only occupied the
surface of the coating. Whatever effect the short wavelengths had
deeper into the coating would be greatly attenuated on playback anyway
(this is the main reason why you can't record to 0dbVU at 10KHz on
anything other than a professional machine running at 15 or 30 ips).

Since the optimum bias level depends on the wavelength of the
recorded signal, stronger for long wavelengths and weaker for short
wavelengths, applying the bias from the back of the tape would provide
a graduated bias level across the thickness of the coating were the
gradient would better match the recorded wavelengths. The bias field
would be strongest deep into the coating where the longer wavelengths
resided and weaker at the record head contact surface where the short
wavelengths largely reside and have most influence on replay
performance.

Assuming the practice matched theory, the crossfield bias provided
extended HF response whilst simultaneously reducing distortion across
the whole spectrum (bias level conventionally applied being a
compromise between minimum distortion and good HF recording
sensitivity).

Whilst Akai and Tandbergh were the only proponents of this system,
afaik (I can't recall which of them won the squabble over the patent
rights), Akai (possibly the loser) made it all rather moot with the
introduction of their Glass Crystal Focussed Field heads (both
play/record and record only flavours) where they insisted the bias
zone was much more sharply focussed in their publicity blurb,
abandoning crossfield bias altogether afterwards.

I rather suspect the improvements offered by the additional
complexity of a crossfield bias head were of a marginal nature to
begin with, possibly becoming ever more marginalised by the
introduction of higher coercivity/remnance coatings that could be
applied as a much thinner layer where the shorter wavelengths could
penetrate to a proportionally greater depth.

There is, one has to assume, _some_ element of truth in the claim
that the new GX heads provided a more focussed field, but I rather
suspect this aspect was 'Bigged Up' by the publicity department.
However, there's no disputing the other benefits of durability, less
scrape noise, accurate gap geometry (only compared to laminated
mu-metal pole pieces - not the ordinary ferrite heads) and reduced
dust accumulation from the tape coating during record and playback.

If for no other reason alone, those GX heads will continue to stand
as a lasting legacy to the name of Akai in the annals of analogue
magnetic recording technology. The effects of Akai's bean counters,
otoh, won't[1].


[1] Other than the fact that they gave me the opportunity to earn
myself a very large helping of "Fully Justified Smugness Points"(tm)
over the issue of the cheapened dolby B encoding / decoding boards in
the GX630DB. Said smugness arising out of my working out what
components had been removed to save a few pennies and, not only that,
but also calculating the correct resistor values, confirmed several
months later when I was looking at the classic dolby B circuit
published in an issue of the "Wirelss World" magazine. Boy! Was I
smug... If smugness could be displayed on a meter, mine would have
had the needle wrapped around the end stop marked "Smug Bastard" when
I read that article. ;-))

[Roderick Stewart]

On Fri, 29 Mar 2013 12:43:22 -0700 (PDT), Curtis Interruptus
<curtisth...@gmail.com> wrote:

>The dot patterning to which I assume that you refer, is caused when
>there is a fixed mathematical relationship between the CSC and line
>frequencies. (283.75 in the original 625/50 PAL). Older readers may
>know this frequency as (F)nat. The precision offset of 25Hz was added
>resulting in (F)csc. The septics got round the same issue by changing
>the Frame rate by 1% (hence 525/59.940.

It's actually 0.1%, it's a reduction of the scanning rate of the
entire signal, not just the field rate, and it had nothing to do with
the inter-frame cancellation of the subcarrier dot pattern which is
the reason for the 25Hz offset to the subcarrier frequency on 625 PAL.
The numbers just happen to work out so as to provide the neccessary
cancellation anyway on 525 NTSC, so that offset isn't necessary.

The reason for the 0.1% offset on 525 NTSC is to do with transmission,
not the signal itself. It's to make the difference between the
subcarrier frequency and the sound carrier an odd multiple of half the
line frequency, to minimise the effects of interfernce between them.
In this case, the numbers happen to be right for 625 but not for 525.
Personally I think it's a shame they didn't offset the sound carriers
of the transmitters instead, as the awkward frame rate made standards
conversion more complicated, but that's hindsight for you.

Rod.

[Roderick Stewart]

On Fri, 29 Mar 2013 20:40:58 +0000 (GMT), charles
<cha...@charleshope.demon.co.uk> wrote:

>you mentioned Fnat, so I assume you learned things at the BBC. I don't
>think anyone else used it - or even knew what it was.

Please Sir! I do! It's 4.4296875MHz.

I'm not sure whether to be proud or embarrassed that I can still
remember that.

Rod.

[Johny B Good]

On Fri, 29 Mar 2013 22:33:27 -0000, "Max Demian"
<max_d...@bigfoot.com> wrote:

>"Johny B Good" <johnny...@invalid.ntlworld.com> wrote in message
>news:g1tbl8tigloeq58a3...@4ax.com...
>

====snip====

>> Ultrasonic AC bias and erase, provided the solution to all of the
>> above shortcomings. Although an AC signal approximately ten times the
>> maximum recording signal level isn't normally regarded as being a bias
>> of any sort in any other system, the name stuck by virtue of its
>> original function in magnetic recorders and an absence of a ready to
>> hand substitute word to replace it.
>
>Reminds me of my old Grundig Cub recorder, with spool drive, DC bias and
>permanent magnet erase, which worked surprisingly well, for speech at any
>rate. I think that there were some really cheap cassette recorders that used
>DC bias and erase.

I was just reviewing this thread (it's gone awfully quiet) when this
last paragraph caught my eye.

That describes exactly a cheap "No Name (that I can recall)" battery
operated portable tape recorder that I'd bought sometime around
'66/'67 at a shop in Liverpool called "Super Radio" located at the top
end of Whitechappel (long since relocated to Dale Street a few
hundred yards away and now trading as PRS (Progressive Radio Supplies
tel: 0151 236 0891 - that number is ingrained in my memory
forevermore). I believe I paid the princely sum of 12 quid for it
which, back then, was princely indeed! :-(

I still have a 3 inch reel of triple play tape with a recording of a
late night ghost story broadcast by Radio Caroline sometime in 1967.
The tape recorder it was made with has long since been consigned to
Land Fill so I can only audition it at a standard speed where it
either sounds very flat at 1 7/8 ips or quite obviously chipmunky at 3
3/4 ips. My best guess at the original recording speed would be a
surprisingly consistent approximation to 2 1/2 ips, give or take.

I recently auditioned it last month when I discovered it amongst a
collection of other 3 inch reels of tape (most of which were
recordings made on a Philips portable (capstain driven) tape recorder)
that I discovered in a biscuit tin hidden away in the attic. One day
RSN, I plan on digitising it (and any other such recordings as I might
find) and resample the wav file to correct the speed error.

I was hoping that there would be a trace of 4 or 5 KHz heterodyne to
help in re-establishing the original speed but of that there was
absolutley no trace (I guess my homebrewed superhet transistor radio
was just too selective to allow such interference). It's going to be a
case of "Adjusting by Ear" when I do get hold of the Round Tuit.

[hwh]

On 3/31/13 4:51 AM, Johny B Good wrote:
> I still have a 3 inch reel of triple play tape with a recording of a
> late night ghost story broadcast by Radio Caroline sometime in 1967.

> One day
> RSN, I plan on digitising it (and any other such recordings as I might
> find) and resample the wav file to correct the speed error.
>
> I was hoping that there would be a trace of 4 or 5 KHz heterodyne to
> help in re-establishing the original speed but of that there was
> absolutley no trace (I guess my homebrewed superhet transistor radio
> was just too selective to allow such interference).

There could be a 9 kHz tone. You never know.
Anyway, there are people collecting old Caroline recordings. They would
be grateful for the restored version.

gr, hwh

[Roger Wilmut]

In article <5334769...@audiomisc.co.uk>,

Jim Lesurf <no...@audiomisc.co.uk> wrote:


> I can't recall if the Blattnerphone or wire recorders used AC bias. But
> over the history of magnetic recording people have repeatedly tried not
> using any AC bias. They can generally get it to work on a lab bench. But in
> practice is it like trying to balance a pencil on its tip to make it work
> well! Any slight variations in the magnetic material, etc, upset the
> results.
>
> Slainte,
>
> Jim

The Blattnerphone and its successor the Marconi-Stille used DC bias.
There were a number of different wire recorders, using both types (wire
was rarely used in broadcasting, at least in the UK) - the 1940 Armour
was one which used AC bias though others, particularly those intended
for dictation or portable use, used DC.

As far as I can see all the coated-tape recorders, starting with the
Magnetophon from 1940 onwards, all used AC bias. I don't see that there
was resistance to its use: it was known in the USA pre-war but at the
time the recording equipment wasn't good enough for the difference to be
noticeable. Some Magnetophons were captured and brought to the UK in
1945 and subsequently several were used by the BBC; the EMI BTR1 was
based on its technology.

Sources: 'Magnetic Recording' by S.J.Begun (Murray Hill, 1949), BBC
Engineering Division Training Manual 1942.

[Stephen]

"Roderick Stewart" <rj...@escapetime.myzen.co.uk> wrote in message
news:q47dl89vhprfiodp7...@4ax.com...

They actually did offset the sound carriers for the BBC test transmissions
using NTSC colour on 405 lines. The numbers aren't right for 405 lines
either because the 3.5 MHz sound carrier is 345.679.. times line frequency.
They offset the sound carrier by 3.25 kHz for colour, increasing it to 346
times, or 3.503250 MHz.

[Johny B Good]

On Sun, 31 Mar 2013 08:20:36 +0200, hwh
<iime...@hotmail.com.invalid> wrote:

>On 3/31/13 4:51 AM, Johny B Good wrote:
>> I still have a 3 inch reel of triple play tape with a recording of a
>> late night ghost story broadcast by Radio Caroline sometime in 1967.
>> One day
>> RSN, I plan on digitising it (and any other such recordings as I might
>> find) and resample the wav file to correct the speed error.
>>
>> I was hoping that there would be a trace of 4 or 5 KHz heterodyne to
>> help in re-establishing the original speed but of that there was
>> absolutley no trace (I guess my homebrewed superhet transistor radio
>> was just too selective to allow such interference).
>
>There could be a 9 kHz tone. You never know.

Ah yes, I was confusing AM's modulation bandwidth in a 9KHz spaced
system. The carrier heterodyne should have been 9KHz. I doubt, even at
2.5 ips, the tape recorder would have been able to record such a high
frequency (not helped by the narrow selectivity of the RX).

>Anyway, there are people collecting old Caroline recordings. They would
>be grateful for the restored version.

That's interesting. I thought it would only be of interest to me
alone as a piece of personal nostalgia. I'll keep that in mind when
I've restored the recording.

[hwh]

On 3/31/13 5:26 PM, Johny B Good wrote:
> Ah yes, I was confusing AM's modulation bandwidth in a 9KHz spaced
> system. The carrier heterodyne should have been 9KHz. I doubt, even at
> 2.5 ips, the tape recorder would have been able to record such a high
> frequency (not helped by the narrow selectivity of the RX).

Very likely.

>> Anyway, there are people collecting old Caroline recordings. They would
>> be grateful for the restored version.
>
> That's interesting. I thought it would only be of interest to me
> alone as a piece of personal nostalgia. I'll keep that in mind when
> I've restored the recording.

More information at:
http://www.azanorak.com/

gr, hwh

[J. P. Gilliver (John)]

In message <966dl8dj5m4ro6lfa...@4ax.com>, Roderick

There's something at the Vintage Wireless museum that has wire-recorder
spools combined with a record-player mechanism; I don't know much about
it (I was looking round on my own, Gerry being downstairs), though I'd
say it was designed as a combined unit rather than being an add-on.
--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

Don't play "stupid" with me... I'm better at it.

[J. P. Gilliver (John)]

In message <533476e...@audiomisc.co.uk>, Jim Lesurf

<no...@audiomisc.co.uk> writes:
>In article <g1tbl8tigloeq58a3...@4ax.com>, Johny B Good
><johnny...@invalid.ntlworld.com> wrote:
>
>
>> [1] Alternatively the other analogy commonly used was that it was akin
>> to the 'crossover distortion' that would ensue in a class B amplifier
>> lacking the necessary bias required to avoid the 'dead zone'.
>
>That's an interesting analogy as *Perfect* class-B would not give any
>crossover distortion as described by theory. But reality tends to defeat
>this hope once you go beyond any kind of lab demo that is tweaked with
>insane levels of care and attention. :-)
>
>Slainte,
>
>Jim
>

I didn't know perfect class B actually existed; I thought it was always,
in practice, class AB.

[SpamTrapSeeSig]

In article <doqdl85lsmtau1cpp...@4ax.com>, Johny B Good
<johnny...@invalid.ntlworld.com> writes

>
>[1] Other than the fact that they gave me the opportunity to earn
>myself a very large helping of "Fully Justified Smugness Points"(tm)
>over the issue of the cheapened dolby B encoding / decoding boards in
>the GX630DB. Said smugness arising out of my working out what
>components had been removed to save a few pennies and, not only that,
>but also calculating the correct resistor values, confirmed several
>months later when I was looking at the classic dolby B circuit
>published in an issue of the "Wirelss World" magazine. Boy! Was I
>smug... If smugness could be displayed on a meter, mine would have
>had the needle wrapped around the end stop marked "Smug Bastard" when
>I read that article. ;-))

Was that the same circuit in the Linsley-Hood Dolby add-on unit? If so,
I've still got the reprint upstairs I think. That reprint collection
also has a pretty decent compressor and some other handy circuits IIRC.
--
SimonM

[Jim Lesurf]

In article <84lfDCD8...@soft255.demon.co.uk>, J. P. Gilliver (John)

<G6...@soft255.demon.co.uk> wrote:
> In message <533476e...@audiomisc.co.uk>, Jim Lesurf
> <no...@audiomisc.co.uk> writes:
> >In article <g1tbl8tigloeq58a3...@4ax.com>, Johny B Good
> ><johnny...@invalid.ntlworld.com> wrote:
> >
> >
> >> [1] Alternatively the other analogy commonly used was that it was
> >> akin to the 'crossover distortion' that would ensue in a class B
> >> amplifier lacking the necessary bias required to avoid the 'dead
> >> zone'.
> >
> >That's an interesting analogy as *Perfect* class-B would not give any
> >crossover distortion as described by theory. But reality tends to
> >defeat this hope once you go beyond any kind of lab demo that is
> >tweaked with insane levels of care and attention. :-)

> I didn't know perfect class B actually existed; I thought it was always,
> in practice, class AB.

Indeed. In practice Class B is too evanescent and fragile to have any
useful existence. Hard enough to balance a pencil on its tip without it
being held or supported. Impossible when you then want then the pencil to
write a message...

[J. P. Gilliver (John)]

In message <5335785...@audiomisc.co.uk>, Jim Lesurf

<no...@audiomisc.co.uk> writes:
>In article <84lfDCD8...@soft255.demon.co.uk>, J. P. Gilliver (John)
><G6...@soft255.demon.co.uk> wrote:
>> In message <533476e...@audiomisc.co.uk>, Jim Lesurf
>> <no...@audiomisc.co.uk> writes:
>> >In article <g1tbl8tigloeq58a3...@4ax.com>, Johny B Good
>> ><johnny...@invalid.ntlworld.com> wrote:
>> >
>> >
>> >> [1] Alternatively the other analogy commonly used was that it was
>> >> akin to the 'crossover distortion' that would ensue in a class B
>> >> amplifier lacking the necessary bias required to avoid the 'dead
>> >> zone'.
>> >
>> >That's an interesting analogy as *Perfect* class-B would not give any
>> >crossover distortion as described by theory. But reality tends to
>> >defeat this hope once you go beyond any kind of lab demo that is
>> >tweaked with insane levels of care and attention. :-)
>
>> I didn't know perfect class B actually existed; I thought it was always,
>> in practice, class AB.
>
>Indeed. In practice Class B is too evanescent and fragile to have any
>useful existence. Hard enough to balance a pencil on its tip without it
>being held or supported. Impossible when you then want then the pencil to
>write a message...
>
>Slainte,
>
>Jim
>

I didn't know it could be created at all, in an amplification sense: I
thought all practical circuits had some distortion near the cutoff
(where the signal crosses zero). [I've said "in an amplification sense"
as I think precision rectifiers can be constructed for instrumentation
purposes.]

--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

Never be haughty to the humble; never be humble to the haughty. -Jefferson
Davis, confederate president (1808-1889)

[John Williamson]

A pefect class B amplifier can be made in theory, if you have
transistors with a zero switch-on time, and other components with an
infinite bandwidth. The distortion in practical circuits is caused by
the time it takes for the transistors to switch on in response to the
signal, and by non-linearities in the frequency response of the required
feedback loop.

Normally, the best compromise is class AB, where the transistors are
biased to just start conducting. Good efficiency, and reasonable quality.

A lot of modern amplifiers are class D, which has the transistors
operating as HF switches, and not as variable resistances.

--
Tciao for Now!

John.

[Jim Lesurf]

In article <fzSnxzWu...@soft255.demon.co.uk>, J. P. Gilliver (John)

<G6...@soft255.demon.co.uk> wrote:
> In message <5335785...@audiomisc.co.uk>, Jim Lesurf
> <no...@audiomisc.co.uk> writes:

> >> >
> >> >That's an interesting analogy as *Perfect* class-B would not give
> >> >any crossover distortion as described by theory. But reality tends
> >> >to defeat this hope once you go beyond any kind of lab demo that is
> >> >tweaked with insane levels of care and attention. :-)
> >
> >> I didn't know perfect class B actually existed; I thought it was
> >> always, in practice, class AB.
> >
> >Indeed. In practice Class B is too evanescent and fragile to have any
> >useful existence. Hard enough to balance a pencil on its tip without it
> >being held or supported. Impossible when you then want then the pencil
> >to write a message...
> >
> >Slainte,
> >
> >Jim
> >
> I didn't know it could be created at all, in an amplification sense: I
> thought all practical circuits had some distortion near the cutoff
> (where the signal crosses zero).

You've over-extended my use of 'perfect'. :-) No amplifier - class A, AB,
etc, that I know of has *no* distortion in practice. Despite simplified
models (like that for the orginal 'current dumping') that seem to show
otherwise.

The distinction between B and AB is that the no-signal condition bias
current in the output devices is *just* reduced to zero, and any signal at
all causes some current in one device, or the other, but never both of
them.

Not that either B or AB would have 'no distortion'.

You can set up a lab demo and tweak the circuit to get arbitrarily close to
class B when there is little or no signal. But even in this situation the
required conditions tend to wander about. Hence the analogy with trying to
balance a pencil on its tip. Add a significant signal level and things get
worse...

In practice therefore even 'class B' amps often tended to be AB when in
actual use. But with such poorly controlled behaviour as to give poor
results.

[Jim Lesurf]

In article <artdhv...@mid.individual.net>, John Williamson

<johnwil...@btinternet.com> wrote:
> On 01/04/2013 13:06, J. P. Gilliver (John) wrote:
> > In message <5335785...@audiomisc.co.uk>, Jim Lesurf
> > <no...@audiomisc.co.uk> writes:


> A pefect class B amplifier can be made in theory,

Yes, in theory all kinds of things are possible... which turn out to be
impractical in reality.

> if you have transistors with a zero switch-on time, and other components
> with an infinite bandwidth. The distortion in practical circuits is
> caused by the time it takes for the transistors to switch on in response
> to the signal, and by non-linearities in the frequency response of the
> required feedback loop.

Slight modification: You'd need zero response time. Or *exactly* the same
response time for both output devices of a pair. Otherwise infinite
bandwidth won't save you. :-)

And, alas, a response time of zero isn't sufficient. You also have the
problem that in real-world devices the devices tend to change behaviour
with temperature or as a result of their recent history of behaviour. This
is particularly significant with real-world audio signals which often are
far from symmetric. So the device temperatures do not remain equal over a
range of timescales.

Plus any variations in, say, the rail voltages that aren't common will tend
to affect the two devices in slightly different ways.

Etc....

> A lot of modern amplifiers are class D, which has the transistors
> operating as HF switches, and not as variable resistances.

A confusing factor here is that we now have many 'switching' amps that use
different logical topologies/methods. So there are actually a number of
different designs which are only covered by being the same 'class' by
making that classes definition sufficiently vague and sweeping.

[Steve Thackery]

Jim Lesurf wrote:

> In practice therefore even 'class B' amps often tended to be AB when
> in actual use.

Indeed. In fact, I'm surprised that anybody thinks this discussion
needs to take place. When I learnt this stuff, it was well known that
'class B' was only a theoretical concept - a kind of 'logical design'
that was interesting and informative to study, whilst acknowledging
that it couldn't be made to work satisfactorily in the real world due
to the real-world limitations in component performance.

Having acknowledged that obvious fact, the discussion then proceeded to
the far more relevant investigation of how far a class B design should
be biased towards 'class A' to get a satisfactory performance /
efficiency trade-off.

This stuff is so obvious, so widely taught, and so well known, it is
surely not a debatable matter, is it?

--
SteveT

[J. P. Gilliver (John)]

In message <477fl85vqv0dibsdv...@4ax.com>, Johny B Good
<johnny...@invalid.ntlworld.com> writes:
[]

> I still have a 3 inch reel of triple play tape with a recording of a
>late night ghost story broadcast by Radio Caroline sometime in 1967.
>The tape recorder it was made with has long since been consigned to
>Land Fill so I can only audition it at a standard speed where it
>either sounds very flat at 1 7/8 ips or quite obviously chipmunky at 3
>3/4 ips. My best guess at the original recording speed would be a
>surprisingly consistent approximation to 2 1/2 ips, give or take.
[]

> I was hoping that there would be a trace of 4 or 5 KHz heterodyne to
>help in re-establishing the original speed but of that there was
>absolutley no trace (I guess my homebrewed superhet transistor radio
>was just too selective to allow such interference). It's going to be a
>case of "Adjusting by Ear" when I do get hold of the Round Tuit.

There might be a trace of mains hum (or second or third or fourth
harmonic thereof) - even if your recorder was battery-powered (was it?),
there'd probably be some pickup from the house, or even on the original
signal, which might have been 60 Hz if Caroline used US generators and
equipment - and not necessarily that stable, but probably enough so to
help establish the speed. The spectrum analyser ("waterfall" I think
it's called) display in GoldWave (or probably most other sound
processing software) would I suspect show it.

--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

Everything in moderation. Including moderation. - Billy Connolly('s website,
according to Radio Times, 14-20 February 2009)

[Johny B Good]

On Mon, 1 Apr 2013 22:14:11 +0100, "J. P. Gilliver (John)"
<G6...@soft255.demon.co.uk> wrote:

>In message <477fl85vqv0dibsdv...@4ax.com>, Johny B Good
><johnny...@invalid.ntlworld.com> writes:
>[]
>> I still have a 3 inch reel of triple play tape with a recording of a
>>late night ghost story broadcast by Radio Caroline sometime in 1967.
>>The tape recorder it was made with has long since been consigned to
>>Land Fill so I can only audition it at a standard speed where it
>>either sounds very flat at 1 7/8 ips or quite obviously chipmunky at 3
>>3/4 ips. My best guess at the original recording speed would be a
>>surprisingly consistent approximation to 2 1/2 ips, give or take.
>[]
>> I was hoping that there would be a trace of 4 or 5 KHz heterodyne to
>>help in re-establishing the original speed but of that there was
>>absolutley no trace (I guess my homebrewed superhet transistor radio
>>was just too selective to allow such interference). It's going to be a
>>case of "Adjusting by Ear" when I do get hold of the Round Tuit.
>
>There might be a trace of mains hum (or second or third or fourth
>harmonic thereof) - even if your recorder was battery-powered (was it?),
>there'd probably be some pickup from the house, or even on the original
>signal, which might have been 60 Hz if Caroline used US generators and
>equipment - and not necessarily that stable, but probably enough so to
>help establish the speed. The spectrum analyser ("waterfall" I think
>it's called) display in GoldWave (or probably most other sound
>processing software) would I suspect show it.

I use CoolEdit Pro which can display a real time spectrum as well as
show a more detailed spectral display gathered from an arbitary length
sample of the wav which I plan to put to such use.

The tape recorder was a battery powered model which is good news from
the point of view of picking out any modulated hum (60 or 50Hz) or,
less likely, since the portable radio was also battery powered, 50Hz
from the local mains supply.

When I auditioned the tape, I could hear no trace of '9Khz'
heterodyne, not even when it was downshifted by the slow playback
speed. This comes as no surpise since my homebrewed transistor
superhet used a 3 stage IF amplifier with adjustable regenerative
feedback employed to improve selectivity on weak signals (not that
Radio Caroline, whether North or South, needed much gain at that time
of night[1]).

If I'm going to detect any constant background signal to use as a cue
to the original speed of the recording, it's most likely to be mains
hum sourced rather than a 9KHz heterodyne.

[1] I often used to listen to Caroline South in the middle of the day
from the Liverpool area just because I could (nothwithstanding the LO
sideband noise effect on such weak signals as I was picking up on the
built in ferrite rod antenna).

[Johny B Good]

On Mon, 1 Apr 2013 13:06:06 +0100, "J. P. Gilliver (John)"

Indeed! I used a couple of op-amps to improve the VU meters on the
GX630DB to get rid of the dead band just below the -20db mark. I had
to adjust the end stop at the bottom of the scale to recalibrate the
-20db point making the original zero point approximate to -30db.

It's wonderful to still be able to meter sub -30db activity instead
of watching a totally dead meter. It nicely shows the recorded disk
warp induced subsonics on pretty well all of my vinyl transfers.

The circuit is pretty simple, the meter, fed by a fullwave bridge
rectifier, is simply placed in series with a suitably chosen feedback
resistor between the output and the inverting input with a suitable
value of resistor going from there to the ground reference point
(non-inverting Hi Z input version). The massive op-amp voltage gain
overcomes the rectifier drop when such rectifier volt drop is within
the feedback network.

This modification was just one of many improvements I made to the
GX630DB

[Jim Lesurf]

In article <rsekl8ljk455sp9du...@4ax.com>, Johny B Good

<johnny...@invalid.ntlworld.com> wrote:


> Indeed! I used a couple of op-amps to improve the VU meters on the
> GX630DB to get rid of the dead band just below the -20db mark. I had to
> adjust the end stop at the bottom of the scale to recalibrate the -20db
> point making the original zero point approximate to -30db.

> It's wonderful to still be able to meter sub -30db activity instead of
> watching a totally dead meter. It nicely shows the recorded disk warp
> induced subsonics on pretty well all of my vinyl transfers.

I'm slightly surprised you get wow subsonics above -30dB - although I
obviously don't know your reference level.

I've transferred a number of my LPs to digital copies using a Tascam
digital recorder. That has a linear bar level indicator with a 60dB span.
The subsonics for LP tend to be down at more like the -50dB level than
anywhere near -30dB.

That said, I'm probably setting the gain so that the RIAA 0dB reference is
well below 0dB on the meters to ensure I record peaks without clipping. [1]
So the subsonics may well approach -30dB in RIAA reference terms. Even
though official 'rumble' values for turntables, etc, tend to be below
-40dB!

One of the advantages of the digital recorder over any analogue deck I've
owned is the excellent metering. The Nak I use does have good meters, but
not as good as the digital recorder. And the digital recorder lets me tweak
settings like decay time for the mean power level and hold time for peak
indicators on a 'project by project' basis.

Slainte,

Jim

[1] I did check this early on using some test LPs. But I've now forgotten
what level I chose!

[Johny B Good]

On Tue, 02 Apr 2013 10:05:54 +0100, Jim Lesurf <no...@audiomisc.co.uk>
wrote:

>In article <rsekl8ljk455sp9du...@4ax.com>, Johny B Good
><johnny...@invalid.ntlworld.com> wrote:
>
>
>> Indeed! I used a couple of op-amps to improve the VU meters on the
>> GX630DB to get rid of the dead band just below the -20db mark. I had to
>> adjust the end stop at the bottom of the scale to recalibrate the -20db
>> point making the original zero point approximate to -30db.
>
>> It's wonderful to still be able to meter sub -30db activity instead of
>> watching a totally dead meter. It nicely shows the recorded disk warp
>> induced subsonics on pretty well all of my vinyl transfers.
>
>I'm slightly surprised you get wow subsonics above -30dB - although I
>obviously don't know your reference level.

Not wow or deck rumble,just the inevitable 2 or 3Hz warp induced
subsonic from the slight warp of the vinyl disk (which is at its
maximum at the start of the groove, fading in level as the stylus
tracks to the innermost part of the groove).

>
>I've transferred a number of my LPs to digital copies using a Tascam
>digital recorder. That has a linear bar level indicator with a 60dB span.
>The subsonics for LP tend to be down at more like the -50dB level than
>anywhere near -30dB.
>
>That said, I'm probably setting the gain so that the RIAA 0dB reference is
>well below 0dB on the meters to ensure I record peaks without clipping. [1]
>So the subsonics may well approach -30dB in RIAA reference terms. Even
>though official 'rumble' values for turntables, etc, tend to be below
>-40dB!

I set the recording level to just below the 0db FSD level for the
maximum peak on a case by case basis for each disk. As long as the
peak level captured is somewhere in the region of -2db and 0db FSD
after removing the obvious loud clicks and pops, I'm done.

If the music content shows evidence of being clipped on some of the
peaks, I'll reduce the level and repeat the capture process unless
it's literally just one or two peaks that suffered a mild amount of
clipping (i.e two or less samples 'pegged' to the FSD clip level). I
very rarely find myself having to do a repeat take.

>
>One of the advantages of the digital recorder over any analogue deck I've
>owned is the excellent metering. The Nak I use does have good meters, but
>not as good as the digital recorder. And the digital recorder lets me tweak
>settings like decay time for the mean power level and hold time for peak
>indicators on a 'project by project' basis.

>

>[1] I did check this early on using some test LPs. But I've now forgotten
>what level I chose!

That's the beauty of using a software meter, no under or over shoot
whatsoever. CoolEdit Pro's metering also allows you to use different
scale ranges (30 to 90db in 15 db increments) has dynamic peak and
valley markers as well as a clip indicator which is very useful (but,
sadly, not for all those PCI and on-board soundcards that were
clipping the line input at -3.5db FSD up until about 5 or 6 years
back).

[Paul Ratcliffe]

On Fri, 29 Mar 2013 17:38:05 +0000, Clive <cl...@yewbank.demon.co.uk> wrote:

> instead of Hanover Blind all that happened was desaturation of the hue
> signal presented to the CRT.

The CRT only deals with RGB. The colour difference signals and luminance
signal are presented to the YUV-RGB matrix.