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From: "Phil Allison"
Subject: Re: Acoustic Feedback reduction
X-Newsreader: Microsoft Outlook Express 5.50.4522.1200
Date: Sat, 11 Jan 2003 14:05:54 +1100
NNTP-Posting-Date: Sat, 11 Jan 2003 13:55:31 EST
Organization: Telstra BigPond Internet Services (http://www.bigpond.com)
"Spehro Pefhany" wrote in message
> Many years ago in good old _Wireless World_ (long before "wireless"
> acquired its present meaning(s)) there was a design published for a
> device used to allow higher volume levels in PA systems before
> feedback occurred (with a given microphone). IIRC, they used
> one or two multipliers in a circuit that shifted the audio pitch by
> around 10Hz.
> Has this sort of thing been integrated into a single chip?
** No. The cheapest and best way to frequency shift an audio signal is
I designed a high quality + 5 Hz Audio Frequency Shifter which was
published in Electronics Australia magazine. It used a number of TL074
op-amps and a pair of AD633 multipliers to do the job.
Such a device is ONLY useful in reverberant rooms (most rooms are)
where standing waves are the major cause of acoustic feedback. Where the
acoustic path is short and direct there will be little or no benefit -
except if you perfer a warble to a squeal.
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