🚀 go-pugleaf

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?  ...
> 
> So . . . Does such a thing exist?  If not why not?
> It seems  1) possible  2) useful  3) saleable
> Am I missing something?

I've done live sound work for a few years now.  I am certain that many folx 
such as yourself have thought of such a monster, but I have some thoeries 
as to why it's not out yet.  However, it is a *great* idea!

This may not be much of a factor for large sound companies, but something 
like this seems expensive!  The software (and hardware) for this would seem 
to take quite a bit of time developing, and start out costing loads of 
dough, so that the sound quality would not be compromised, and so that it 
would be easy enough for any sound jockey to use.  Although, I'm sure costs 
could be kept within range of most sound-company budgets with some time.

Also, you'd either have to decide on a specific computer to run it on, or 
develop your own CPU, operating system and user interface to run with the 
unit.  And, if you decided on a computer, should it be a Mac, IBM, etc?  
How many sound companies have road-worthy computers?  Sound gear on the 
road gets *real* banged up during load-ins and -outs.  I don't see an 
efficient way of interfacing with a console to control individual input 
gains.  You'd have to build a patch bay of some sort, or a computer 
interfacing scheme to make the whole thing work, and the most efficient way 
for the computer (the interface) is the most "costly" (not just money), and 
the inefficient (patch-pay method) is old technology.  Am I making sense?

I'm sure there are a few other things that hold back this "technological 
wonder".  I certainly see how a profitable sound company could afford some 
machine like this, cause the best way to go would be to buy a console with 
the computer built-in, but this is a great expense.  The ideal way to go 
(so it would be available to everybody) would be to make it interface with 
present boards, and that is a bit more difficult.

I am open to more discussion on this topic, cause I would certainly like to 
see something like this developed!  

> 
> Randy Brumabugh
> rando@skipper.dfrf.nasa.gov

I hope this fuels a little discussion on the subject for ya, Randy.
-- 
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   Chuck Urwiler    University of Miami Music Engineering   Voice & Keys  
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 chuck@miavax.ir.miami.edu |
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Disclaimer: I only work and learn at this University. I don't speak for it!

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

In article <4762@uafhp.uark.edu> cdc@uafhcx.uucp (C. D. Covington) writes:

> [Much stuff deleted]  They call impulse response an echogram and
>measure it in European concert halls using a 9mm blank pistol!
>
When I took the course in acoustics, I was told that popping a large
balloon works much better than a pistol, because the frequency
distribution is beter.  Gunshots are somewhat deficient in the low
end of frequency.

I also want to point out that there are really two implementations
of this device (feedback assassin) that we could be discussing:
the first is a big, expensive version that sound companies would
want to buy, with complete tweaking of all the parameters.  The
cheaper alternative might be a "black box" which does nothing more
than look for frequency spikes and attenuate them.  This could be
very useful for cases when sound quality is less important than
not having feedback.

Brian Hanafee