[PD] [OT] gallery installation sound
Frank Barknecht
fbar at footils.org
Tue Feb 13 18:10:06 CET 2007
Hallo,
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:
http://lac.zkm.de/2006/papers/lac2006_fons_adriaensen_01.pdf
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.
Ciao
--
Frank Barknecht _ ______footils.org_ __goto10.org__
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