psycho-acoustics (embarrasing)
Doug Kelly
have been concidering getting a receiver with surround sound and junking my amp
/ preamp setup. Somewhat of a downgrade I know but separate surround units are
almost as much $$ and I hate large stacks of equipement. Anyway, I was out
auditioning one (a yamaha) which had an addtional feature I found interesting, a
subwoofer (preamp level) output, as well as dolby surround and several of
yamaha's 'digital processing' mode for night club, concert hall and other
'effects'.
Well, I'm not too hot on such post production processing schemes, but the sales
person was really hyping them so I gave them a listen. He popped in a cd and
began switching modes from normal to various modes. I was surprised and
somewhat relieved at how little they did.... the bad thing is that both myself
and the salesman could 'hear the difference'. Well after about 2 or three mins
of listening I decided to hear it a little louder, reached up, twisted the
volume control and.... Nothing! no difference. I looked confused, the sales
person looked flustered, I turned it all the way down and ... still playing,
same volume!
Well the much embarassed sales person figured out which amp we had been listenin to and, once he got me to stop laughing, auditioned the correct amp. The
surround and 'effects' modes now had a _MUCH_ greater effect on the sound! The
irony of this was however that I really did hear the difference before! ACK!
Doug
--
Douglas Kelly
Illinois State Water Survey
Office of Ground-Water Quality & Contamination
d...@ux1.cso.uiuc.edu
Joe Chelena
DK> Well, I'm not too hot on such post production processing schemes, but the
DK> sales
DK> person was really hyping them so I gave them a listen.
While you are at it give the Hughes SRS system a try. It is the system now being used by Sony and RCA/Thomson for their surround sound TVs. Hughes makes a separate unit, the AK-100, that can be hooked-up to an audio system. I heard an A/B comparison between a Dolby ProLogic system and the SRS system a few weeks back and the ProLogic system really came out on the poor end of the test.
* Origin: My ears are made of tin! (1:109/716.915)
Gary Katch
>I had a really funny thing happen to me saturday that some of you will like. I
...[embarrassing story deleted]
I too have experienced the power of my own mind fooling itself. I
bought the Tilson-Thomas version of Rhapsody in Blue and found it to be
one of the best recordings I have ever heard for realistic soundstaging.
That opening clarinet trill startles me everytime, because I think it's
really there, behind where the wall suddenly disappears. Every
instrument is precisely located and defined as the orchestra and piano
join in.
I invited a friend to share in this wonderful new recording. After the
requisite raving to him (as above) we sat down to enjoy. Yes, said my
friend, truly a wonderful recording. Precise, detailed, good instrument
location.
Later, I noticed something about my amp settings. Earlier I had been
listening to a distant FM station and couldn't stand the noise. Yes,
you guessed it, my friend and I had listened to the Rhapsody entirely
in mono.
-- gk.
Gary Katch / gpk...@alcor.concordia.ca / tel: (514) 848-7632 / fax: 848-7622
CONCORDIA UNIVERSITY / 1455 De Maisonneuve West / Montreal (Quebec) H3G 1M8
Joe Chelena
GK> I too have experienced the power of my own mind fooling itself. I
GK> bought the Tilson-Thomas version of Rhapsody in Blue and found it to be
GK> one of the best recordings I have ever heard for realistic soundstaging.
GK> I invited a friend to share in this wonderful new recording. After the
GK> requisite raving to him (as above) we sat down to enjoy. Yes, said my
GK> friend, truly a wonderful recording. Precise, detailed, good instrument
GK> location.
GK>
GK> Later, I noticed something about my amp settings. Earlier I had been
GK> listening to a distant FM station and couldn't stand the noise. Yes,
GK> you guessed it, my friend and I had listened to the Rhapsody entirely
GK> in Mono.
What????????????????? Mono on a amp, well really a preamp, and mono on a tuner have nothing in common when it comes to reducing FM noise. If the FM signal is noisy setting the preamps output to mono will just give you noisy mono.
Doug M
> GK> listening to a distant FM station and couldn't stand the noise. Yes,
> GK> you guessed it, my friend and I had listened to the Rhapsody entirely
> GK> in Mono.
>
>What????????????????? Mono on a amp, well really a preamp, and mono on a tuner have nothing in common when it comes to reducing FM noise. If the FM signal is noisy setting the preamps output to mono will just give you noisy mono.
> * Origin: My ears are made of tin! (1:109/716.915)
The latter poster has his mouth set to self-righteous and ignorant (they're
usually correlated). Summing the outputs of an FM stereo decoder to mono
(to the extent it's done accurately) will have precisely the same noise-
reduction effect as any "other" technique (assuming one exists) for monoizing
the decoded signal. Unlike the poster, my faulty memory renders me uncertain
on this point, but it's my impression that most decoder chips use nothing
more than this technique for forcing mono. Turning off the 19kHz pilot at
the stereo encoder and mono-izing the transmitted signal (i.e. reducing the
modulation of the 38kHz supressed-subcarrier to zero) will improve the
signal t0 noise ratio of the transmitted signal, but that's not where the
noise in your receiver is coming from.
I really fear for my safety in this increasingly software-mediated world
given the depressing amount of gullibility and stubborn ignorance manifested
in this newsgroup, whose subject matter is pretty damn straightforward.
david n stivers
> GK>
> GK> Later, I noticed something about my amp settings. Earlier I had been
> GK> listening to a distant FM station and couldn't stand the noise. Yes,
> GK> you guessed it, my friend and I had listened to the Rhapsody entirely
> GK> in Mono.
>
>What????????????????? Mono on a amp, well really a preamp, and mono on a tuner>have nothing in common when it comes to reducing FM noise. If the FM signal is
>noisy setting the preamps output to mono will just give you noisy mono.
The "main" signal that an FM receiver receives is mono (L+R). To construct a
stereo signal from a mono signal, it needs a L-R (or R-L) signal, which it gets
from a carrier signal on the same frequency, but modulated at a higher rate
(38kHz I think). The problem is that this higher frequency modulation is
more susceptable to reception problems, and so is usually noisier than the
mono signal. So, what you get is L-R+e, where e represents noise.
Hence, when reconstructing the stereo signal, the output is the sum or
the difference of the mono signal and the L-R signal:
Left output = L' = [(L+R) + (L-R+e)]/2 = L+e/2
Right output = R' = [(L+R) - (L-R+e)]/2 = R-e/2
If e is small, you don't care too much about it, and leave the signal in stereo.
Note that e is out of phase; so, if e is too large, you can make a mono signal
L'+R' = (L+e/2)+(R-e/2) = L+R that has no e in it.
So, theoretically, it doesn't matter whether you throw the mono switch on the
receiver or on the pre-amp; you'll still get the same nice clean mono signal.
In practice, you'll have some extra noise thrown in by the time it gets to
the pre-amp, but it should still be negligible compared the noise in the
broadcast that you wish to excise.
BTW, ever wonder how Muzak, K-Mart shoppers network &c. all get broadcast?
Radio stations will lease out their even higher carrier signals (like at 45kHz).
--
david n stivers st...@rice.edu
Jim Roth
In article <43...@ucbvax.BERKELEY.EDU>, do...@okeeffe.CS.Berkeley.EDU (Doug M) writes...
>> GK> Later, I noticed something about my amp settings. Earlier I had been
>> GK> listening to a distant FM station and couldn't stand the noise. Yes,
>> GK> you guessed it, my friend and I had listened to the Rhapsody entirely
>> GK> in Mono.
>>What????????????????? Mono on a amp, well really a preamp, and mono on a
>> tuner have nothing in common when it comes to reducing FM noise.
>> If the FM signal is noisy setting the preamps output to mono will just
>> give you noisy mono.
>> * Origin: My ears are made of tin! (1:109/716.915)
>The latter poster has his mouth set to self-righteous and ignorant (they're
>usually correlated). Summing the outputs of an FM stereo decoder to mono
>(to the extent it's done accurately) will have precisely the same noise-
>reduction effect as any "other" technique (assuming one exists) for monoizing
>the decoded signal.
I haven't followed this whole thread, but there is a fact about FM stereo
that is worth mentioning.
The noise spectrum out of an FM discriminator has a parabolic or 6 dB/octave
rising noise density when the signal strength is enough to be "above
threshold". Roughly, that means that the zero crossings of the limited
carrier in the IF are clean, so that the only effect of additive
noise on the carrier will be to jitter (Oh-oh, there's that J-word again!)
the zero crossings, or the instantaneous phase of the carrier.
The phase noise has a flat spectrum. But FM is the rate of change of
phase and hence has a 6 dB/octive boost - much like a differentiator.
What does this have to with FM stereo versus FM mono? The L-R sidebands
of the multiplex signal are centered around a 38 kHz carrier - up where
the noise spectrum is boosted by this 6 dB/octave rate. Switching to
stereo thus does much more harm than merely doubling the noise, and
summing to mono will quiet down the background noise of FM reception
by a remarkable amount.
- Jim
david r moran
Double whaaaaat! Mono settings anywhere downstream of stereo FM will
reduce the noise significantly if it is due to weak signal. Not if
the noise is in the source tape or CD or whatever. Original poster did
the right thing, and why are you going on with the question marks? Check it
out for yourself -- disconnect your FM antenna....
As for the psychoacoustic joke, good clear mono over spacious speakers
with the suggestion of stereo (premise) is quite nice and will cause
many of us to think it is nicely spaced left-right -- if this has not
happened already!
Gordon LETWIN
A poster recently stated that switching your amp to mono won't suppress
FM noise, but will just give you mono noisy FM. Another poster corrected
him on this topic.
Although I don't know much about FM or analog electronics, I worked for
Heathkit about 15 years ago and had a friend who was an FM receiver
engineer. He explained that since FM stereo is produced by adding and
subtracting the mono (L+R) base signal with a subcarrier (L-R or R-L, forget),
the noise generated by a weak subcarrier is 180 degrees out of phase in
each channel, so by simply adding the two channels you produce mono and
cancel the noise.
Further, he stated that some RCA engineer first realized this and patented
the technique, so that an FM designer could either hook his "mono" switch
up to some electronics to supress the stereo generation, or he could
pay RCA a royalty and just have the switch short the two channels together.
Heathkit paid the royalty and shorted the signals.
So yes, shorting the signals downstream of the tuner itself will work
just fine...
Gordon Letwin
Andrew Koenig
> What????????????????? Mono on a amp, well really a preamp, and mono on a tuner have nothing in common when it comes to reducing FM noise. If the FM signal is noisy setting the preamps output to mono will just give you noisy mono.
Not true. Try it sometime and see.
There's a good reason for it too: FM stereo is broadcast as L+R in the
normal audio band and L-R frequency-shifted up 15 kHz or so. If you
throw away the L-R, you're also throwing away all the noise that found
its way into that band, so the total amount of noise is reduced.
--
--Andrew Koenig
a...@europa.att.com
jj, like it or not
>have nothing in common when it comes to reducing FM noise. If the FM signal is
>noisy setting the preamps output to mono will just give you noisy mono.
Um, wrong. I wish you'd both looked into the issue a bit more carefully,
AND you'd considered what sort of ammunition a wrong answer for
a techie-appearing person will give the subjectivist types.
FM, at least in the US, is transmitted as L+R and L-R. The way that it
is transmitted, with L-R in a subcarrier at high frequency (remember
the frequency distribution of noise in FM?) and lower energy, ensures that
the L-R signal will have more noise than the L+R signal (the baseband
FM signal that can also be decoded by a mono tuner).
Because of this, the stereophonic FM signal decoded in MONO will
have substantially less noice. Because of this, even a stereo
signal decoded in stereo, and then summed to mono, will have less
noise than the mono channel, even after any inequal treatment of
L and R after the tuner is considered.
If you take out any portion of the L-R signal, you're taking
out a portion of the more noisy signal, and reducing the total
noise as a result.
--
the dale, *Copyright alice!jj 1991, all rights reserved, except transmission
Call the *by USENET and like free facilities granted. Said permission is
Spears of *granted only for complete copies that include this notice.
Annandale *Use on pay-for-read services specifically disallowed.
Unprivileged user
>>reduction effect as any "other" technique (assuming one exists) for monoizing
>>the decoded signal.
Path: okeeffe.CS.Berkeley.EDU!dougm
> Jim Roth:
>The noise spectrum out of an FM discriminator has a parabolic or 6 dB/octave
>rising noise density when the signal strength is enough to be "above
>threshold". Roughly, that means that the zero crossings of the limited
>carrier in the IF are clean, so that the only effect of additive
>noise on the carrier will be to jitter (Oh-oh, there's that J-word again!)
>the zero crossings, or the instantaneous phase of the carrier.
>
>The phase noise has a flat spectrum. But FM is the rate of change of
>phase and hence has a 6 dB/octive boost - much like a differentiator.
>
>What does this have to with FM stereo versus FM mono? The L-R sidebands
>of the multiplex signal are centered around a 38 kHz carrier - up where
>the noise spectrum is boosted by this 6 dB/octave rate. Switching to
>stereo thus does much more harm than merely doubling the noise, and
>summing to mono will quiet down the background noise of FM reception
>by a remarkable amount.
>
>- Jim
Yeah, I think the remarkable amount is around 21 dB.
(That's the extent of my contribution, but for some reason rn thinks
it's sensible to refuse my followup unless I rattle on at least as
long as what I quoted.
Does this mean
I have to fill
as many lines,
or type as many characters,
or what?
How 'bout one of those .sig blocks?
*********************************************************************************************************This is the .sig to Gary's Show*************************************************This is the .sig to Gary's Show*************************************************Gary called me up and asked me*************************
*************************To design it********************************************************************This is the .sig to Gary's Show************************
*************************This is the .sig to Gary's Show*************************************************This is the .sig to Gary*******************************
****************************Shandling's Show!***********************************
**************************[Whistle two verses]******************************************************************************************************************
********************************************************************************
********************************************************************************
P.S. Anyone who can tell me a more sensible way of coping with this feature
will incur my doglike devotion. heh heh
Hey! I got an idea! I could just fill the space with my god-descended
revealed truth about LP's and muenster cable...................................
Well, as Buffalo Bob was reputed to have said, that ought to hold the little
bastards!
________________________________________________________________________________
Dave Medin
Bingo, except the difference channel is a AM sideband modulated subcarrier
at twice the pilot frequency (19 KHz), or 38 KHz.
Because some of the subcarrier noise anti-correlates due to the mathematical
relationship above, switching to mono in the preamp WILL reduce the noise
somewhat (3 - 6 dB in practice).
--
------------------------------------------------------------------------
Dave Medin Voice: (205) 730-5812
Intergraph Corp. (205) 837-1174
M/S CR1104
Madison, AL 35894-0001 Internet: me...@catbyte.b11.ingr.com
*********Everywhere You Look...(at least around my office)***********
*The opinions here are strictly my own (or those of my machine)
Doug M
Because some of the subcarrier noise anti-correlates due to the mathematical
relationship above, switching to mono in the preamp WILL reduce the noise
somewhat (3 - 6 dB in practice).
^^^^^^^^^^^^^^^^^^^^^^
--
>------------------------------------------------------------------------
Dave Medin Voice: (205) 730-5812
Intergraph Corp. (205) 837-1174
M/S CR1104
As has been pointed out, by me and others, this is wrong. *All* of the decoded
noise from the subchannel "anticorrelates" in the sense that in mono it's
simply rejected, discarded, thrown away, not used. Summing the decoded
L + R is equivalent to adding in the decoded subchannel (L-R) and subtracting
it; if the matrix coefficients are accurate and there's no phase-shift
before the summing, it all goes away. And because the subchannel is *MUCH*
noisier than the lower (< 19 kHz) part of the baseband, a mono-ized
signal can be *MUCH* quieter (~21 dB) than a noisy stereo signal. See the
previous remarks about the so-called triangular FM noise spectrum.
Doug Maisel
vcxz...@yahoo.com.cn
appears , why?
thanks!