From: John Woodgate
Subject: Re: Acoustic Feedback reduction
Date: Sat, 11 Jan 2003 19:52:41 +0000
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Sat, 11 Jan 2003 21:47:25 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Phil Allison
wrote (in ) about 'Acoustic
Feedback reduction', on Sat, 11 Jan 2003:
> If you mix
>direct and shifted signals you get beats - loud and clear. If you delay
>the shifted signal by even 3 mS the beats are destroyed. As the PA speakers
>are more than 1 metre away from the performer.......
That's VERY interesting. At 100 Hz, 3 ms is a fraction of a period,
whereas at 1 kHz it's 3 periods. Something that happens over that range
is obviously a significant feature of human psychoacoustics.
If we take, say, 150 Hz and 155 Hz present together, there is a
cyclically-varying phase shift between them, corresponding to the 5 Hz
beat frequency. Adding a 3.33 ms delay adds a 'd.c. component' to this
cyclical variation, 0.5 of a cycle of the 150 Hz, 180 degrees at 150 Hz
or 6 degrees at 5 Hz.
I wonder why that destroys the perception of the beats.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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