Path: utzoo!attcan!uunet!maverick.ksu.ksu.edu!uafhp!uafhcx!cdc
From: cdc@uafhcx.uucp (C. D. Covington)
Newsgroups: comp.dsp
Subject: Re: DSP for feedback control
Summary: Eliminate Feedback with Intelligent DSP
Message-ID: <4762@uafhp.uark.edu>
Date: 12 Jun 90 23:30:53 GMT
References: <539@skipper.dfrf.nasa.gov>
Sender: netnews@uafhp.uark.edu
Followup-To: comp.dsp
Organization: College of Engineering, University of Arkansas, Fayetteville
Lines: 27


In article <539@skipper.dfrf.nasa.gov>, rando@skipper.dfrf.nasa.gov (Randy Brumbaugh) writes:

> Wouldn't it be possible to use DSP to eliminate feedback 
> in real time before it is noticed?  The processor would 
> "look" at the spectral contents of the program and watch
> for any "runaway" frequency bands, where the energy is 
> increasing exponentially (??).  It could also check for 

    This is a great idea that lots of people have had over the years
but we are all waiting on the cost to get down.  In order to do a good
job, lots of bits are needed to keep the quantization noise down.
I even went to the trouble of measuring the impulse response of my
church's sanctuary.  Very impressive.  I then took a *long* FFT of the
results.  More impressive.  Troublesome resonances tend to be *very*
narrowband due to the distances involved.  Of course if anyone turns
their head - all bets are off.  The system needs to be very fast in
producing good parametric estimates of the feedback path characteristics.

     What I have thought of is an array of possible suboptimal solutions.
I did spend a great deal of time at the library studying architectural
acoustics.  I had no idea people took it all that seriously.  You ought
to look up a few references.  They call impulse response an echogram and
measure it in European concert halls using a 9mm blank pistol!

C. David Covington (WA5TGF)  cdc@uafhcx.uark.edu     (501) 575-6583
Asst Prof, Elec Eng          Univ of Arkansas        Fayetteville, AR 72701