Time variance and sweep speed influence swept sine measurements. With maximum length sequence (MLS) techniques such effects are also noticeable. These MLS papers may be of interest to you:
U. Peter Svensson, Johan L. Nielsen, "Errors in MLS measurements caused by time-variance in acoustic systems," J. Audio Eng. Soc. 47, pp. 907-927 [1999].
P. Svensson, J. L. Nielsen, "Short-term time-variance in electroacoustic channels and its effects on MLS measurements," in Proc. of the 15th International Congress on Acoustics, Trondheim, Norway, pp. IV: 163-166 [1995].
Best regards,
Mendel Kleiner Perhaps it's obvious, but I have to mention it because no one else has. The sweep should be longer than the response that is being measured. For a room, one second is pretty short. For an HRTF, probably ok. For concert halls we often use 4-8 seconds, which gives good signal to noise ratios, but is not so long that the likelihood of an interupting noise becomes high. Have you asked Farina? I'm sure he would be happy to advise. Best,
Philip
On 26 Jul 2015 10:46, "Neeraj Sharma" < neerajww@xxxxxxxxx> wrote: I just did some RIR measurement in a varechoic chamber. Interesting to find a discussion on it here. I use the following specifications.
(Will be happy to know if there are guidelines to be followed for proper RIR measurements, especially if a database is to be released)
1. Linear (constant amplitude) sine sweep (20-20 kHz) 2. Logarthim (constant amplitude) sine sweep (20-20 kHz). 3. Sweep duration 20 sec, Fs = 48 kHz 4. Ambient room noise of -50 dB (can be lowered a bit more)
5. Microphones and speakers are at least 100 cm above ground (to reduce low frequency dominance)
6. A small powerful speaker. (the speaker is however not omnidirectional, and has no separate HF and LF diaphragm)
7. Omni-directional mics facing the speaker
8. Temperature of 25 degree celsius
Remarks:
a. The RT60 with Linear and Log sweep is quite close (difference within 100 msec).
b. Peak speaker volume results in harmonics of the sweeps, this can affect the RIR, and RT60. Hence, it is important to be sure that no harmonics are created by speaker. c. I will not consider smaller duration sweep as an alternative to longer duration even under the burden of computation.
Best regards,
Neeks
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