E-mail: support
Date: 29 Nov 2004
Time: 12:03:12
From: Calvert Dayton
E-mail: support
Date: 29 Nov 2004
Time: 12:03:12
Martin,
Without knowing specifics of how you were making your measurement, I would guess that the discrepancies you saw were a result of differences in data acquisition techniques. If you saved an impulse acquired in WinMLS as a wave file and opened it in Smaart Acoustic Tools, or opened one of your Smaart-measured impulse responses in WinMLS you should find the STI results reported by the two programs to be nearly identical, given identical data.
If you're acquiring data in Smaart Acoustic Tools using the Dual-FFT transfer function with random noise as your stimulus, be aware that this particular combination tends to let more "room" into the measurement than MLS or TDS, which is interesting in some respects but also decreases the effective S/N of the measurement. And since STI is essentially a frequency-dependent measure of S/N, a "noisier" measurement will naturally result in a lower STI.
To approach the kind of noise rejection in a random noise measurement that you get with MLS, you probably need to up the number of averages and/or FFT size significantly (to increase the S/N ratio of the measurement). Alternately, you could use a synchronous test signal instead of random noise as your stimulus for Dual-FFT measurements, which should give you the same kind of noise rejection you get with MLS (without the downside of MLS's over-sensitivity to time variance).