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From: "Phil Allison"
References: <96dU9.21919$jM5.email@example.com> <firstname.lastname@example.org>
Subject: Re: Acoustic Feedback reduction
X-Newsreader: Microsoft Outlook Express 5.50.4522.1200
Date: Mon, 13 Jan 2003 11:01:22 +1100
NNTP-Posting-Date: Mon, 13 Jan 2003 10:50:54 EST
Organization: Telstra BigPond Internet Services (http://www.bigpond.com)
"Don Pearce" wrote in message
> On Mon, 13 Jan 2003 00:20:58 +1100, "Phil Allison"
> >"Don Pearce" wrote in message
> >> On Sun, 12 Jan 2003 23:33:10 +1100, "Phil Allison"
> >> wrote:
> >> > The number of persons I have had to FIGHT with over this
> >> >terminology issue is appalling - they all think that frequency and
> >> >mean the same thing.
> >> >
> >> > Pitch shifting is of course of NO use in feedback supression.
> >> >
> >> >
> >> > ................... Phil
> >> First - I am not looking for a fight.
> > ** But I am gonna give you one Mr Expert.
> >> But - the only difference between pitch shifting and frequency
> >> shifting is that in pitch shifting, each frequency is shifted by a
> >> certain percentage of itself, while in frequency shifting each
> >> frequency is shifted by a given number of Hz.
> > ** THAT is one HELL of a difference.
> Not in the context - both do indeed necessitate a frequency shift.
** Bull, it is massive in context. Stick to RF Don. One cannot use
pitch shift in a PA system to reduce feedback.
> >> The two are different in one important regard - in pitch shifting the
> >> harmonic relationships are preserved and the result remains musical.
> >> In frequency shifting this does not happen, and if the shift is
> >> carried too far, the result is very unmusical.
> > ** A few Hz upshift has no detectable impact on most ears.
> Depends on the frequency. At low frequency a few Hz shift could
> represent a semitone - decidedly detectable.
** Not on music programme. Only on tones and only if quickly A-B ed.
> Shame you decided to start out by being rude. Especially as in the
> rest of the post you haven't really contradicted anything I said -
> merely expanded on it.
** I contradicted the whole stupid lot.
There are a few areas of specific error in your
> last section, though. The main one is your confusion between
> reverberation and standing waves. They are not the same thing and a
> space can be highly reverberant with no standing waves whatever.
** Complete bullshit. What planet do you come from ?
You have clearly never seen the *slow* sweep response of an
auditorium - it is full of sharp peaks and dips. What do you suspect
causes them? Men from Mars ?
Ever done a slow response sweep of a digital reverb unit - guess what -
same peaks and dips - guess why ???
And> of course your arbitrary limits of 4 to 20Hz have no meaning.
** Only to a moronic jerk like you Don. These are the lowest frequency
standing waves that can be supported in auditoria and rooms where a PA might
be used. All other standing waves are derived from these by integer
> And of course there are resonant structures that affect howl frequency
> besides the room.
** The room is the one with the really high Q resonances - several
thousand of them with Qs in the thousands at high frequencies.
The loudspeakers and microphones are a mass of
> resonant peaks themselves. Being able to shift the feedback tone off
> the top of one of these peaks can give you an extra few dBs of margin
> in the onset of feedback.
** No, the peaks in them are too broad. It makes practically no
difference - plus they are not evenly spaced by a fixed number of Hz like in
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