[PD] [OT] gallery installation sound

Frank Barknecht fbar at footils.org
Tue Feb 13 18:10:06 CET 2007

Hans-Christoph Steiner hat gesagt: // Hans-Christoph Steiner wrote:

> Usually acoustic measurements are done with impulses, AFAIK.  An  
> ideal impulse actually has all frequencies in it, so it's useful for  
> that kind of thing.  Plus it's easy to differentiate between the  
> initial signal and the room effects just based on time.

Actually I think, engineers prefer to use frequency sweeps instead of
pulses nowadays. The problem with pulses is, that they are hard to get
right: You need a clean pulse and a very silent environment: 

   The main problem with using Dirac pulses in
   an acoustical measurement is that as a result of
   their very short duration and finite amplitude,
   they contain very little energy, and measure-
   ment accuracy will be limited by the signal to
   noise ratio of the equipment used and of the
   system itself. While it is possible to use Dirac
   pulses reproduced by a loudspeaker in the con-
   trolled environment of an acoustics laboratory,
   this is all but infeasible in most real life situa-
   tions, e.g. for measuring a room or concert hall,
   where there will always be background noises of
   some sort.

This is from Fons Adriaensen's LAC paper:

Fons then explains sine sweeps as an alternative method: 

   The advantage of using a sweep is that at any
   time we produce only a single frequency, and
   any distortion introduced will consist of the har-
   monics of that frequency only. If we use a rising
   frequency sweep, the harmonics will be gener-
   ated ahead of the same frequencies appearing
   in the signal. So after deconvolution, any dis-
   tortion will appear as spurious peaks in negative
   time in the impulse response, and most of it can
   then be edited out easily.

This method's origin according to Fons is a paper by A. Farina:

  Angelo Farina. 2000. Simultanuous measurement of impulse response
  and distortion with a swept-sine technique. Audio Engineering
  Society Preprint 5093.

It is implementes in Fons' ALIKI software, that he presented at LAC2006.

 Frank Barknecht                 _ ______footils.org_ __goto10.org__

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