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__