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Morset Sound Development
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Electro-acoustical measurements
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Please post your messages related to electro-acoustical measurements
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Subject Optimal signal for measuring systems
Date
Tue Nov 19 2002 23:04
Author Lars Morset
(morset@winmls.com)
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Dear Mr. Hagenbach,
thanks for your questions.
>I would like more specific information about why log sweep >is better than any other presently used signal.
I am not saying it is best in all cases (the SynAudCon mailing list has had a good discussion about this issue), MLS still has advantages. The main reasons a log swept sine is favorable are:
1. Robustness against Time Variance. A single sine sweep obviously gives the best robustness against time variance simply because it sends out only one frequency at a time. If you have problems with time variance, then make sure you use only one single sweep. If you use linear or logarithmic doesn't matter for the time variance.
2. You can use a high output signal. A logarithmic sine sweep has the great feature that the harmonic distortion is separated from the linear part of the impulse response. This allows you to drive the loudspeaker harder than you can with e.g. MLS. The effective crest factor is also better than MLS and much better than e.g. pink noise. The log sweep also has a pink amplitude distribution, which is desired e.g. when measuring a room that will also have apprx. pink background noise amplitude distribution.
For more information, please see the download section under training:
http://www.nvo.com/winmls/nss-folder/training/
There you will find the two documents
LectureSweptSineMLS.ppt and
Swept-sineAndMLS_LarsMorset.doc
Let me know if you find them useful.
>Has Peter Svensson written any papers et-cetera on log sweep >vs MLS vs TDS? If so how could I get them?
He and Johan Nielsen (in charge of the room acoustics part of WinMLS) recently won a AES award "best paper written by authors below 35 years" for their paper on MLS and effects of time variance. I will let him know that you may be interested in his papers.
He has not yet written anything about swept sine measurements, but he is following the work we do, and I often ask for his advice.
About TDS I must say again that we don't have any experience with it, we have used MLS instead (as is most common in Europe) and now with the "new" log sine sweep method I see no advantage in using TDS. I want the impulse response as the result, TDS does not give me that. That’s another reason why I have not spent time on investigating it. When you have the impulse response you are free to do all kinds of post-processing (frequency and phase response, reverberation time, etc...)
Best regards,
Lars
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