Olin,

We had talked about using removable acoustic panels of some sort,=20
removable just to avoid the possibility of mold forming from the=20
moisture, or something like that. That may be the simplest solution,=20
overall.

OK, this DSPic thing is kind of a neat and creative idea, and DSP is=20
something I am interested in, but haven't really had any time or real=20
reason to look at. I have read about it and the things you can do with=20
it. It's probably impractical for me to pursue this in reality, but it=20
is interesting.

couple of questions:

    * I don't know much about DSP. Could you explain to me what you mean
      when you say "a true impulse is of course impossible" ? I guess
      you are saying that it would be impossible to excite the
      room/environment over the complete range completely accurately?

    * I have a PC program that can measure the "frequency response" of
      the room. I have used it in the past to detect at what frequencies
      feedback begins to occur, to help with "ringing out" a system and
      adjusting the EQ. Maybe another way to approach it is to sweep
      through the relevant part of the audio band and note the amplitude
      at various levels?
    * Let's say one wanted to apply some kind of 'impulse" to the
      room....how could you go about that? Thump on the wall? Run some
      kind of signal through a speaker or some other kind of transducer?
      What would be the character of that "impulse" ?

Thanks,

Mark Skeels
Engineer
Competition Electronics, Inc.
TEL: 815-874-8001
FAX: 815-874-8181
www.competitionelectronics.com

On 5/17/2011 9:39 AM, Olin Lathrop wrote:
> Mark E. Skeels wrote:
>> What I am looking for is a way to mic several individuals standing in
>> 3 feet of water, in close proximity, in a small room with lousy
>> acoustics, and still get a nice full sound.
> First, I would do as much as possible to improve the sound characteristic=
s
> of the room.  The sound is probably a mess because it's bouncing around w=
ith
> little attenuation in a small room.  That will set up standing waves at
> certain frequencies.  Put some sort of accoutic absorbers on any surface =
you
> can.  Hopefully at least the ceiling is available for that.
>
> Fancy sound deadening materials are available for professional studios, b=
ut
> these will be expensive.  You can get surprisingly far with off the shelf
> materials and some ingenuity.  For example, I once saw a room with cardbo=
ard
> egg cartons stapled to the walls.  It deadened the sound surprisingly wel=
l,
> although it wasn't like a professional sound studio.  Multiple thin sheet=
s
> of cloth with a little separation between them takes space but are
> relatively cheap.
>
> After that, it depends on how much effort you want to put in.  The room i=
s a
> linear system from the point of view of sound out someone's mouth to it
> arriving at a microphone.  In theory, whatever transform is applied by th=
is
> system can be reversed.  In practise, you can make it a lot better but it
> will never be perfect.  The transform will change for different source
> locations, and measuring it in the first place isn't easy.  Ideally you p=
ut
> out a impulse and measure the response at the mic, but a true impulse is =
of
> course impossible so there are tradeoffs and compromises.  Just measuring
> the frequency response with good resolution over the audio range you want=
 to
> reproduce is probably the best practical approach.
>
> Once you have the frequency response, it's just math to convert that to t=
he
> convolution kernel of a finite impulse response filter, which you then
> implement in a dsPIC.  Let's say you sample at 20KHz rate.  A dsPIC can d=
o
> up to 40M multiply-accumulates per second.  That means 2000 MAC per 20KHz
> sample.  That's 100ms of sound, or 33m of propagation.  That's more than
> necessary, so it passes the first level sanity check.  Of course the dsPI=
C
> will have to do a few other things than just running MACs, but there is
> enough headroom for things to work out.
>
>
> ********************************************************************
> Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
> (978) 742-9014.  Gold level PIC consultants since 2000.
--=20
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