jargon

[RichD]

What's the difference between reverb, echo, and feedback?


--
Rich

[John Fields]

On Fri, 18 Nov 2011 13:51:37 -0800 (PST), RichD
<r_dela...@yahoo.com> wrote:

>What's the difference between reverb, echo, and feedback?

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

Reverberation is the persistence of sound in a particular space after
the original sound is removed.[1] A reverberation, or reverb, is
created when a sound is produced in an enclosed space causing a large
number of echoes to build up and then slowly decay as the sound is
absorbed by the walls and air.


http://en.wiktionary.org/wiki/echo#Noun

A reflected sound that is heard again by its initial observer.


http://www.thefreedictionary.com/feedback

Sound created when a transducer such as a microphone or electric
guitar picks up sound from a speaker connected to an amplifier and
regenerates it back through the amplifier.
--
JF

[Phil Allison]

"Rich Dope"

> What's the difference between reverb, echo, and feedback?

** Depends on the context.

Digital delays and tape echo machines have controls with these names.



... Phil

[VWWall]

Or, in an electrical circuit, when the voltage or current at a point in
the circuit is "fed back" to a point earlier in the circuit. Depending
on its phase, this can be either negative or positive feedback.

--
Virg Wall

[k...@att.bizzzzzzzzzzzz]

On Fri, 18 Nov 2011 13:51:37 -0800 (PST), RichD <r_dela...@yahoo.com>
wrote:

>What's the difference between reverb, echo, and feedback?

Delay

[RichD]

On Nov 18, "k...@att.bizzzzzzzzzzzz" <k...@att.bizzzzzzzzzzzz> wrote:
> >What's the difference between reverb, echo,  and feedback?
>
> Delay

Aren't they all delay?

--
Rich

[k...@att.bizzzzzzzzzzzz]

On Fri, 18 Nov 2011 16:56:56 -0800 (PST), RichD <r_dela...@yahoo.com>
wrote:

Different delay (and decay). If the delay is on the order of a wavelength and
shorter than the decay, it's feedback. Greater than that it's reverb until
you can distinguish the individual images. Then it's echo. ...at least
that's how I see it.

[Don Pearce]

On Fri, 18 Nov 2011 13:51:37 -0800 (PST), RichD
<r_dela...@yahoo.com> wrote:

>What's the difference between reverb, echo, and feedback?

Echo is a single reflection of a sound - the kind you hear when you
shout "Hello" near a cliff.

If you put together many echoes, arriving from different distances
into a jumble that you can't distinguish - that is reverb. You get
that in, say, a large church.

Feedback is a situation you only get when you have an amplifier and a
speaker. The sound arriving from the speaker is a little louder than
the one that originally hit the microphone, so that comes out of the
speaker a little louder still. This loop will build until the system
howls. You cure it by turning down the amplifier so the sound from the
speaker is always a little softer than the original when it hits the
microphone.

d

[Trevor]

"Don Pearce" <sp...@spam.com> wrote in message
news:4ec76c2...@news.eternal-september.org...

> On Fri, 18 Nov 2011 13:51:37 -0800 (PST), RichD
> <r_dela...@yahoo.com> wrote:
>
>>What's the difference between reverb, echo, and feedback?
>
> Echo is a single reflection of a sound - the kind you hear when you
> shout "Hello" near a cliff.

Multiple reflections are also common in such instances.

> Feedback is a situation you only get when you have an amplifier and a
> speaker. The sound arriving from the speaker is a little louder than
> the one that originally hit the microphone, so that comes out of the
> speaker a little louder still. This loop will build until the system
> howls.

That would be *acoustic feedback* only, There are MANY other types of
course.

>You cure it by turning down the amplifier so the sound from the
> speaker is always a little softer than the original when it hits the
> microphone.

Or any other method that reduces the loop gain at the feedback frequency,
notch filtering being a common example.

Trevor.

[Don Pearce]

On Sat, 19 Nov 2011 20:22:43 +1100, "Trevor" <tre...@home.net> wrote:

>
>"Don Pearce" <sp...@spam.com> wrote in message
>news:4ec76c2...@news.eternal-september.org...
>> On Fri, 18 Nov 2011 13:51:37 -0800 (PST), RichD
>> <r_dela...@yahoo.com> wrote:
>>
>>>What's the difference between reverb, echo, and feedback?
>>
>> Echo is a single reflection of a sound - the kind you hear when you
>> shout "Hello" near a cliff.
>
>Multiple reflections are also common in such instances.
>

No they are not. One cliff, one echo. No choice.

>
>> Feedback is a situation you only get when you have an amplifier and a
>> speaker. The sound arriving from the speaker is a little louder than
>> the one that originally hit the microphone, so that comes out of the
>> speaker a little louder still. This loop will build until the system
>> howls.
>
>That would be *acoustic feedback* only, There are MANY other types of
>course.
>

In the context of the question it would simply be confusing to discuss
- or even mention - other kinds.

>
>>You cure it by turning down the amplifier so the sound from the
>> speaker is always a little softer than the original when it hits the
>> microphone.
>
>Or any other method that reduces the loop gain at the feedback frequency,
>notch filtering being a common example.
>

Again, given the question, no need to complicate the answer.

d

[Dick Pierce]

On Nov 19, 12:12 am, "k...@att.bizzzzzzzzzzzz"

<k...@att.bizzzzzzzzzzzz> wrote:
> RichD <r_dela...@yahoo.com>
> wrote:
>
>> On Nov 18, "k...@att.bizzzzzzzzzzzz" <k...@att.bizzzzzzzzzzzz> wrote:
>>
>>>> What's the difference between reverb, echo, and feedback?

Perhaps we might ask the original poster what
is meant by "reverb" and "echo" and "feedback."

By "echo" and "reverb," do you mean the acoustical
phenomenon of echo and reverberation? Or do you mean
the analog or digital effects (simulations, if you
will) often labelled "echo" and "reverb"?

"Feedback" is, in some ways, an effect that's in a
different class. But all systems with a connection
between the output and the input are capable of having
feedback, By "feedback," are you talking about when
a system, breaks into self-oscillation, which means
positiive, regenerative feedback?

>> Aren't they all delay?
>
>
> Different delay (and decay). If the delay is on the order of a wavelength and
> shorter than the decay, it's feedback.

Wrong. Feedback requires two conditions: first, the delay
must be an integral multiple of a wavelength (or complete
phase rotations: essentially equivalent) and second, the
system must have a power gain equal to or greater than one.
Feedback cannot occur unless both conditions are present.
The requirement of gain in the system is what makes feedback
very different than either echo or reverb.

The notion that feedback requires a delay on the order of
a wavelength is easily shown to be false when one observes
acoustical feedback in amplified PA systems happening at
middle frequencies (several hundred to several thousand
Hertz) where the amplifier and speaker are quite some
distance apart, many dozens of feet, where the corresponding
delay between the two corresponds to many wavelengths.

In such a situation, one very quick cure is to turn the
volume down: this reduces the overall gain of the system
to less than 1, and the regnerative feedback then stops.
There's still feedback, but without the necessary gain,
the system no longer oscillates.

> Greater than that it's reverb

So, is there some specific delay value in which you claim
that an echo becomes reverb?

--
+--------------------------------+
+ Dick Pierce |
+ Professional Audio Development |
+--------------------------------+

[sgo...@changethisparttohardbat.com]

The original post sounded like a homework question.

[Don Pearce]

On 19 Nov 2011 16:40:38 GMT, sgo...@changethisparttohardbat.com
wrote:

>The original post sounded like a homework question.

I'm not so sure. The feedback part was too far out of kilter with the
rest for any real physics teacher to have set it.

d

[sgo...@changethisparttohardbat.com]

I was thinking of a recording class in a music department.

In rec.audio.tech Don Pearce <sp...@spam.com> wrote:
: On 19 Nov 2011 16:40:38 GMT, sgo...@changethisparttohardbat.com

[Don Pearce]

On 19 Nov 2011 17:26:59 GMT, sgo...@changethisparttohardbat.com
wrote:

Ah. That probably makes it worse, not better.

d

[Kaz Kylheku]

On 2011-11-19, Don Pearce <sp...@spam.com> wrote:
> On Fri, 18 Nov 2011 13:51:37 -0800 (PST), RichD
><r_dela...@yahoo.com> wrote:
>
>>What's the difference between reverb, echo, and feedback?
>
> Echo is a single reflection of a sound - the kind you hear when you
> shout "Hello" near a cliff.
>
> If you put together many echoes, arriving from different distances
> into a jumble that you can't distinguish - that is reverb. You get
> that in, say, a large church.
>
> Feedback is a situation you only get when you have an amplifier and a
> speaker. The sound arriving from the speaker is a little louder than
> the one that originally hit the microphone, so that comes out of the
> speaker a little louder still. This loop will build until the system
> howls.

That is positive feedback. Feedback is not always positive.

If there is a lot of distance between the speaker and microphone,
you can hear echos rather than howls.

Feedback can be (but does not have to be) used for generating echos and
reverbs in effect units or software.

In digital effects units, feedback is used to make it look like there is more
RAM. Rather than computing all echoes from the original input function (which
requires enough RAM to store a window of sound representing the longest echo
time) the echos are faked by taking the output and feeding a fraction of it
back to the input. The same is done for faking long reverbs.

I have an old Yamaha unit here from 1989 which has only a 700 ms delay,
but the reverb can be cranked to 40 seconds, haha. Any sample you hear beyond
700 ms, related to the original signal, has already been through the digital
mill and is reappearing via feedback. Accordingly, the reverb starts to sound
like crap beyond 2 seconds.

A honestly modeled 40 second reverb would actually have an impulse response
sample of 40 seconds from a nice sounding hall, and use a 40 second window of
the input to do the convolution.

[k...@att.bizzzzzzzzzzzz]

On Sat, 19 Nov 2011 03:11:23 -0800 (PST), Dick Pierce
<dpierce.ca...@gmail.com> wrote:

>On Nov 19, 12:12 am, "k...@att.bizzzzzzzzzzzz"
><k...@att.bizzzzzzzzzzzz> wrote:
>> RichD <r_dela...@yahoo.com>
>> wrote:
>>
>>> On Nov 18, "k...@att.bizzzzzzzzzzzz" <k...@att.bizzzzzzzzzzzz> wrote:
>>>
>>>>> What's the difference between reverb, echo, and feedback?
>
>Perhaps we might ask the original poster what
>is meant by "reverb" and "echo" and "feedback."
>
>By "echo" and "reverb," do you mean the acoustical
>phenomenon of echo and reverberation? Or do you mean
>the analog or digital effects (simulations, if you
>will) often labelled "echo" and "reverb"?
>
>"Feedback" is, in some ways, an effect that's in a
>different class. But all systems with a connection
>between the output and the input are capable of having
>feedback, By "feedback," are you talking about when
>a system, breaks into self-oscillation, which means
>positiive, regenerative feedback?
>
>>> Aren't they all delay?
>>
>>
>> Different delay (and decay). If the delay is on the order of a wavelength and
>> shorter than the decay, it's feedback.
>
>
>Wrong.

Disagree.

>Feedback requires two conditions: first, the delay
>must be an integral multiple of a wavelength (or complete
>phase rotations: essentially equivalent)

No, it can be sub-wavelength. Half wavelength would essentially be negative
feedback. There is no reason why feedback must be exactly in phase.

>and second, the
>system must have a power gain equal to or greater than one.

To regenerate, sure. There was nothing here about regeneration.

>Feedback cannot occur unless both conditions are present.

Oscillation cannot occur unless the gain at 360degrees is greater >1. Feedback
certainly can.

>The requirement of gain in the system is what makes feedback
>very different than either echo or reverb.

You're conflating "feedback" and "oscillation" (regenerative feedback).

>The notion that feedback requires a delay on the order of
>a wavelength is easily shown to be false when one observes
>acoustical feedback in amplified PA systems happening at
>middle frequencies (several hundred to several thousand
>Hertz) where the amplifier and speaker are quite some
>distance apart, many dozens of feet, where the corresponding
>delay between the two corresponds to many wavelengths.

Ok, I'll buy that regeneration can occur at > 1 wavelength.

>In such a situation, one very quick cure is to turn the
>volume down: this reduces the overall gain of the system
>to less than 1, and the regnerative feedback then stops.

^^^^^^^^^^^^^^^^^^^^
Oscillation stops but feedback continues

>There's still feedback, but without the necessary gain,
>the system no longer oscillates.

Ok, you've admitted that you're confusing feedback and oscillation.

>> Greater than that it's reverb
>
>So, is there some specific delay value in which you claim
>that an echo becomes reverb?

When you can hear it, but not discern the individual images (echo). There is
obviously a gray area there.

[k...@att.bizzzzzzzzzzzz]

On Sat, 19 Nov 2011 10:16:43 GMT, sp...@spam.com (Don Pearce) wrote:

>On Sat, 19 Nov 2011 20:22:43 +1100, "Trevor" <tre...@home.net> wrote:
>
>>
>>"Don Pearce" <sp...@spam.com> wrote in message
>>news:4ec76c2...@news.eternal-september.org...
>>> On Fri, 18 Nov 2011 13:51:37 -0800 (PST), RichD
>>> <r_dela...@yahoo.com> wrote:
>>>
>>>>What's the difference between reverb, echo, and feedback?
>>>
>>> Echo is a single reflection of a sound - the kind you hear when you
>>> shout "Hello" near a cliff.
>>
>>Multiple reflections are also common in such instances.
>>
>
>No they are not. One cliff, one echo. No choice.

Two walls of said cliff; multiple echoes. If you're on the edge of the cliff
with no opposing wall there will be zero echo.

>>> Feedback is a situation you only get when you have an amplifier and a
>>> speaker. The sound arriving from the speaker is a little louder than
>>> the one that originally hit the microphone, so that comes out of the
>>> speaker a little louder still. This loop will build until the system
>>> howls.
>>
>>That would be *acoustic feedback* only, There are MANY other types of
>>course.
>>
>In the context of the question it would simply be confusing to discuss
>- or even mention - other kinds.
>>
>>>You cure it by turning down the amplifier so the sound from the
>>> speaker is always a little softer than the original when it hits the
>>> microphone.
>>
>>Or any other method that reduces the loop gain at the feedback frequency,
>>notch filtering being a common example.
>>
>
>Again, given the question, no need to complicate the answer.

But you found it necessary to bring up loop gain. Interesting. You wouldn't
be an audiophool, by chance?

[Don Pearce]

On Sat, 19 Nov 2011 12:17:35 -0600, "k...@att.bizzzzzzzzzzzz"
<k...@att.bizzzzzzzzzzzz> wrote:

>On Sat, 19 Nov 2011 10:16:43 GMT, sp...@spam.com (Don Pearce) wrote:
>
>>On Sat, 19 Nov 2011 20:22:43 +1100, "Trevor" <tre...@home.net> wrote:
>>
>>>
>>>"Don Pearce" <sp...@spam.com> wrote in message
>>>news:4ec76c2...@news.eternal-september.org...
>>>> On Fri, 18 Nov 2011 13:51:37 -0800 (PST), RichD
>>>> <r_dela...@yahoo.com> wrote:
>>>>
>>>>>What's the difference between reverb, echo, and feedback?
>>>>
>>>> Echo is a single reflection of a sound - the kind you hear when you
>>>> shout "Hello" near a cliff.
>>>
>>>Multiple reflections are also common in such instances.
>>>
>>
>>No they are not. One cliff, one echo. No choice.
>
>Two walls of said cliff; multiple echoes. If you're on the edge of the cliff
>with no opposing wall there will be zero echo.
>

Since when does one cliff have two walls? The cliff IS the wall.

>>>> Feedback is a situation you only get when you have an amplifier and a
>>>> speaker. The sound arriving from the speaker is a little louder than
>>>> the one that originally hit the microphone, so that comes out of the
>>>> speaker a little louder still. This loop will build until the system
>>>> howls.
>>>
>>>That would be *acoustic feedback* only, There are MANY other types of
>>>course.
>>>
>>In the context of the question it would simply be confusing to discuss
>>- or even mention - other kinds.
>>>
>>>>You cure it by turning down the amplifier so the sound from the
>>>> speaker is always a little softer than the original when it hits the
>>>> microphone.
>>>
>>>Or any other method that reduces the loop gain at the feedback frequency,
>>>notch filtering being a common example.
>>>
>>
>>Again, given the question, no need to complicate the answer.
>
>But you found it necessary to bring up loop gain. Interesting. You wouldn't
>be an audiophool, by chance?

Loop gain greater than unity is what causes feedback howl. There is no
way of avoiding it if you want to explain what causes the feedback.
And make no mistake, the feedback the OP was asking about was the loud
howl you get when you turn the PA up too far.

d

[k...@att.bizzzzzzzzzzzz]

On Sat, 19 Nov 2011 18:23:36 GMT, sp...@spam.com (Don Pearce) wrote:

>On Sat, 19 Nov 2011 12:17:35 -0600, "k...@att.bizzzzzzzzzzzz"
><k...@att.bizzzzzzzzzzzz> wrote:
>
>>On Sat, 19 Nov 2011 10:16:43 GMT, sp...@spam.com (Don Pearce) wrote:
>>
>>>On Sat, 19 Nov 2011 20:22:43 +1100, "Trevor" <tre...@home.net> wrote:
>>>
>>>>
>>>>"Don Pearce" <sp...@spam.com> wrote in message
>>>>news:4ec76c2...@news.eternal-september.org...
>>>>> On Fri, 18 Nov 2011 13:51:37 -0800 (PST), RichD
>>>>> <r_dela...@yahoo.com> wrote:
>>>>>
>>>>>>What's the difference between reverb, echo, and feedback?
>>>>>
>>>>> Echo is a single reflection of a sound - the kind you hear when you
>>>>> shout "Hello" near a cliff.
>>>>
>>>>Multiple reflections are also common in such instances.
>>>>
>>>
>>>No they are not. One cliff, one echo. No choice.
>>
>>Two walls of said cliff; multiple echoes. If you're on the edge of the cliff
>>with no opposing wall there will be zero echo.
>>
>Since when does one cliff have two walls? The cliff IS the wall.

Zero intelligence.

>>>>> Feedback is a situation you only get when you have an amplifier and a
>>>>> speaker. The sound arriving from the speaker is a little louder than
>>>>> the one that originally hit the microphone, so that comes out of the
>>>>> speaker a little louder still. This loop will build until the system
>>>>> howls.
>>>>
>>>>That would be *acoustic feedback* only, There are MANY other types of
>>>>course.
>>>>
>>>In the context of the question it would simply be confusing to discuss
>>>- or even mention - other kinds.
>>>>
>>>>>You cure it by turning down the amplifier so the sound from the
>>>>> speaker is always a little softer than the original when it hits the
>>>>> microphone.
>>>>
>>>>Or any other method that reduces the loop gain at the feedback frequency,
>>>>notch filtering being a common example.
>>>>
>>>
>>>Again, given the question, no need to complicate the answer.
>>
>>But you found it necessary to bring up loop gain. Interesting. You wouldn't
>>be an audiophool, by chance?
>
>Loop gain greater than unity is what causes feedback howl. There is no
>way of avoiding it if you want to explain what causes the feedback.

Wrong. *Regenerative* feedback needs a gain > unity.

>And make no mistake, the feedback the OP was asking about was the loud
>howl you get when you turn the PA up too far.

You can't even keep *your* terms straight. You *must* be an audiophool (lack
of an answer speaks volumes).

[Kaz Kylheku]

On 2011-11-19, Don Pearce <sp...@spam.com> wrote:

> And make no mistake, the feedback the OP was asking about was the loud
> howl you get when you turn the PA up too far.

It rather looked like the OP was asking about studio effects (in which
"feedback" is a parameter: e.g. delay with nonzero feedback creates repeating
echo.)

[Don Pearce]

On Sat, 19 Nov 2011 18:05:11 -0600, "k...@att.bizzzzzzzzzzzz"

I leave the verdict to the audience.

d

[Arny Krueger]

"Don Pearce" <sp...@spam.com> wrote in message

news:4ec8970...@news.eternal-september.org...

There is no doubt that your answer was correct, Don.

KRW's response was one of those hard-to-understand pronouncements of "you
are wrong" followed by a recitation of the same identical facts. Since his
facts agree with you, his pronouncement that you were wrong is itself wrong.

Obviously, he's not watching very closely.

There was a rush to judgment.

He owes you an apology.

[Phil Allison]

"Don Pearce"

> And make no mistake, the feedback the OP was asking about was the loud
> howl you get when you turn the PA up too far.

** The wording of his massively ambiguous post does not suggest that.

Effects units that delay an audio signal become " reverb " units with the
aid of some feedback from output to input.

That is the "jargon" used.



... Phil

[k...@att.bizzzzzzzzzzzz]

He's illiterate.

>KRW's response was one of those hard-to-understand pronouncements of "you
>are wrong" followed by a recitation of the same identical facts. Since his
>facts agree with you, his pronouncement that you were wrong is itself wrong.

He is absolutely wrong. He can't even follow his own definitions.

>Obviously, he's not watching very closely.

You audiophools are some piece of work.

>There was a rush to judgment.
>
>He owes you an apology.

Absolutely wrong.

[Trevor]

"Don Pearce" <sp...@spam.com> wrote in message

news:4ec7817b...@news.eternal-september.org...

>>> Echo is a single reflection of a sound - the kind you hear when you
>>> shout "Hello" near a cliff.
>>
>>Multiple reflections are also common in such instances.
>>
>
> No they are not. One cliff, one echo. No choice.

In the real world cliffs are not usually one straight smooth edge of course.

>>> Feedback is a situation you only get when you have an amplifier and a
>>> speaker. The sound arriving from the speaker is a little louder than
>>> the one that originally hit the microphone, so that comes out of the
>>> speaker a little louder still. This loop will build until the system
>>> howls.
>>
>>That would be *acoustic feedback* only, There are MANY other types of
>>course.
>>
> In the context of the question it would simply be confusing to discuss
> - or even mention - other kinds.

If you prefer to simplify things so much you at least need to point that
out.

>>>You cure it by turning down the amplifier so the sound from the
>>> speaker is always a little softer than the original when it hits the
>>> microphone.
>>
>>Or any other method that reduces the loop gain at the feedback frequency,
>>notch filtering being a common example.
>>
>
> Again, given the question, no need to complicate the answer.

Or simplify it to the point of being wrong. To paraphrase Einstein, things
should be as simple as possible, not simpler.

Trevor.

[Rich Grise]

Trevor wrote:
> "Don Pearce" <sp...@spam.com> wrote in message

>>>> Echo is a single reflection of a sound - the kind you hear when you
>>>> shout "Hello" near a cliff.
>>>
>>>Multiple reflections are also common in such instances.
>>
>> No they are not. One cliff, one echo. No choice.
>
> In the real world cliffs are not usually one straight smooth edge of
> course.
>

That's why an echo is cool - they're relatively rare. :-)

Cheers!
Rich

[Don Pearce]

On Mon, 21 Nov 2011 11:44:56 +1100, "Trevor" <tre...@home.net> wrote:

>
>"Don Pearce" <sp...@spam.com> wrote in message
>news:4ec7817b...@news.eternal-september.org...
>>>> Echo is a single reflection of a sound - the kind you hear when you
>>>> shout "Hello" near a cliff.
>>>
>>>Multiple reflections are also common in such instances.
>>>
>>
>> No they are not. One cliff, one echo. No choice.
>
>In the real world cliffs are not usually one straight smooth edge of course.
>

My mistake. I thought I was talking about a hypothetical cliff. I now
find I was in fact talking about a cliff that you know personally, and
has multiple faces. Would you care to introduce me to it so I can
perform a mathematical analysis? That will obviously make things much
simpler for the OP.

>
>>>> Feedback is a situation you only get when you have an amplifier and a
>>>> speaker. The sound arriving from the speaker is a little louder than
>>>> the one that originally hit the microphone, so that comes out of the
>>>> speaker a little louder still. This loop will build until the system
>>>> howls.
>>>
>>>That would be *acoustic feedback* only, There are MANY other types of
>>>course.
>>>
>> In the context of the question it would simply be confusing to discuss
>> - or even mention - other kinds.
>
>If you prefer to simplify things so much you at least need to point that
>out.
>

I was doing what anybody would do when explaining a principle,
reducing it to its minimum implementation. It's what you do.

>
>>>>You cure it by turning down the amplifier so the sound from the
>>>> speaker is always a little softer than the original when it hits the
>>>> microphone.
>>>
>>>Or any other method that reduces the loop gain at the feedback frequency,
>>>notch filtering being a common example.
>>>
>>
>> Again, given the question, no need to complicate the answer.
>
>Or simplify it to the point of being wrong. To paraphrase Einstein, things
>should be as simple as possible, not simpler.
>

Simplified to the point of being wrong? Hear feedback, turn the gain
down until it stops. You are going to have to explain what is wrong
here - clearly I'm being thick.

d

[Trevor]

"Don Pearce" <sp...@spam.com> wrote in message

news:4eca866e...@news.eternal-september.org...

>clearly I'm being thick.

Something we can agree on then! :-)

Trevor.