Subject RASTI measurement Date Fri Aug 9 2002 00:15 Author Tim Leung (2207leung@hknet.com)
Can I know if pink noise is only type of test signal for RASTI measurement? Can I use MSL for RASTI measurement? Thanks in advance.

Subject WinMLS can indeed measure RASTI Date Tue Aug 13 2002 21:44 Author Johan L. Nielsen (johan.nielsen@c2i.net)

Hi Tim The normal signal for RASTI measurement is a specially modulated noise signal, according to the IEC 60268-16 standard. The standard also mentions the possibility of using an MLS signal, in which case the modulations are not appropriate. Using WinMLS you can measure impulse responses with MLS, and one of several post processing options is calculation of RASTI. You will find this under Room Acoustics->Parameter Settings. With this technique the full STI can be calculated after spending the same amount of measurement time. We therefore recommend that the STI is used instead of, or at least in addition to, the RASTI parameter. For further information, see the WinMLS user's guide. Best wishes Johan L. (responsible for WinMLS room acoustics development)

	Subject Radiation Pattern measurements Date Tue Sep 17 2002 05:39 Author Bob Hagenbach (rchagenbach@hotmail.com)
If I was going to do loudspaeker pattern measurements (amlpitude and phase) at a long distance (100 meters) what system would give the best S/N ratio? WinMLS, MLS TEF Smart Thanks for your time

	Subject Radiation Pattern measurements Date Sun Sep 22 2002 05:56 Author Bob Hagenbach (rchagenbach@hotmail.com)
Lars could you elaborate on your answer? For example, why does WinMLS give a better S/N ratio than TEF. I was under the impression that TEF was the winner in that department.

Subject Be aware of time variance Date Sat Sep 21 2002 08:46 Author Lars Morset (morset@winmls.com)

Dear Bob, thanks for your question. Is the desired result polar plot at specific frequencies (not in octave bands)? If you are interested in obtaining the impulse response (from which you can calculate polar plots, frequency response and so on) I would recommend the new logarithmic swept sine available in the new WinMLS beta version. This method is better than MLS for long distance measurements (because of the robustness to time-variance due to wind and temperature gradients). WinMLS is optimized to get the best SNR for the chosen measurement method for such type of measurements. I would find it strange if any system would give a better SNR for a MLS or log swept sine excitation. I would recommend a high quality sound card to get the best results. Best, Lars

Subject time-variance Date Fri Nov 15 2002 20:04 Author Bob Hagenbach (rchagenbach@mail.gbronline.com )

Lars, You replied: "I would recommend the new logarithmic swept sine available in the new WinMLS beta version. This method is better than MLS for long distance measurements (because of the robustness to time-variance due to wind and temperature gradients)." The main problem with long distance (greater than 10 meters) radiation pattern measurements is temperature gradients can literally blow the signal around. This make amplitude measurements very hard and phase measurements impossible. That is presently why loudspeaker manufacturers do not do phase measurements. It seems like some type of reference acoustical channel is needed to compensate for temperature gradients. I do not understand how any measurement technique (TEF, MLS, dual channel FFT or log sweep) can compensate for changing atmospheric conditions.

Subject Be aware of time variance Date Sun Sep 22 2002 06:00 Author Bob Hagenbach (rchagenbach@hotmail.com)

Lars, I want a measurement system that will give me the following "raw" data at each frequency (not smoothed data. i.e. octave, 1/3 octave et-cetera) and angle 1) In-phase part 2) Quadrature part I want to be able to put a “time window” around the direct sound so I can remove any reflections. Does the width of the time window affect the speed of the measurement like the present implimentation of TDF (TEF20) does? Being able to post process the data, after I gather it, so I could produce the following information would be nice. 1) Amplitude vs. Frequency response 2) Phase vs. Frequency response 3) Impulse response 4) Doublet response (Hilbert transform of Impulse response)

Subject Features Date Tue Oct 1 2002 11:02 Author Lars Morset (morset@winmls.com)

Bob, thanks for your questions. 1) In-phase part 2) Quadrature part [Lars Morset] The new beta can plot the real and imaginary part. I want to be able to put a “time window” around the direct sound so I can remove any reflections. Does the width of the time window affect the speed of the measurement like the present implimentation of TDF (TEF20) does? [Lars Morset] You can window the impulse response after the measurement as a post-processing. Please note that we are not using any kind of tracking window in WinMLS during the measurement. If you want the impulse response as result, I do not see the advantage with using a tracking window. 1) Amplitude vs. Frequency response 2) Phase vs. Frequency response 3) Impulse response [Lars Morset] This you can do with WinMLS. 4) Doublet response (Hilbert transform of Impulse response) [Lars Morset] WinMLS plots the Energy-Time-Curve, which I think is similar to. Because some of the terms you use are new to me, I had to consult professor Peter Svensson about this. His answer is as follows: "I don't think that some of these quantities are relevant for an impulse response measurement system. When you calculate the transfer function as the FFT of the impulse response, you get the complex value of the transfer function. But this is probably not what you are asking for?" If you have further comments or questions, please post them. If you want to direct questions to prof. Svensson, he said he was willing to answer them. Best, Lars

	Subject Log sweep vs MLS vs linear sweep Date Fri Nov 15 2002 19:57 Author Bob Hagenbach (rchagenbach@hotmail.com)
I would like more specific information about why log sweep is better than any other presently used signal. Has Peter Svensson written any papers et-cetera on log sweep vs MLS vs TDS? If so how could I get them?

	Subject Exponentially swept sine measurements Date Sun Mar 9 2003 17:02 Author John Mulcahy (nospam@nowhere.com) File: Measuring impulse resp and distortion with swept sine 134-AES00.pdf
Attached is a good paper on the advantages of exponentially swept sine measurements.

Subject Optimal signal for measuring systems Date Tue Nov 19 2002 23:04 Author Lars Morset (morset@winmls.com)

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

Subject MLS vs TDS Date Wed Nov 20 2002 09:49 Author Peter Svensson (svensson@tele.ntnu.no)

>Has Peter Svensson written any papers et-cetera on log sweep >vs MLS vs TDS? If so how could I get them? No, I have not compared these methods. I have studied the MLS method specifically and found that it is indeed sensitive to time-variance which leads to problems in large rooms and very large problems outdoors. There have been some papers on the log sweep method, most notably by Müller & Passarini in JAES vol. 49, pp. 443-471 (2001). Best regards, Peter Svensson

Subject measuring STI Date Fri Dec 13 2002 10:36 Author Petra Larm (Petra.Larm@ttl.fi)

Hi, I'm going to use winmls to measure speech transmission index and I've some questions which arose when learning the evaluation version: 1 According to the Help file there should be Room Acoustics measure settings option but I didn't find it. I've checked this Measurement setups Toolbar and the options are: -ImpulseExcitation -Master Setup -QuasiRealTimeAnalyzer -RoomLarge -RoomLarge2Microphones -RoomSmall -RunFromMatlab -SoundCardVX222-VXPocket -SoundSystemOptimalization -SterSetup -THD+Noise(1kHz) -ViolinAcoustics but no RoomAcoustics settings. Should I use Master Setup? 2 Speech/noise correction: Are the speech and noise values that I put there assumed to be those that would arise in non-reverberant conditions? If so, why can I measure the noise level with sound level meter? (In reverberant conditions) Can I use speech level values that I get by subtracting the influence of the distance from the speaker to the microphone from the standard speech spectrum values? 3 What is this Gaussian emphasis that has been mentioned in the STI notes (found in the web site)? Is it taken account in winmls? Thank You... With kind regards Petra Larm

Subject On speech/noise correction for STI Date Mon Jan 6 2003 22:53 Author Johan L. Nielsen (johan.nielsen@c2i.net)

> 2 Speech/noise correction: Are the speech and noise values that I put > there assumed to be those that would arise in non-reverberant > conditions? If so, why can I measure the noise level with sound level > meter? (In reverberant conditions) Can I use speech level values that I > get by subtracting the influence of the distance from the speaker to the > microphone from the standard speech spectrum values? The speech and noise levels that make up the so-called MTF correction are supposed to be measured at the receiver position, under reverberant conditions. The speech level is hence the total level; direct sound, reflections and reverberation, and no correction for distance should be made. The noise level is the ambient noise. I was really puzzled by this question at first, and had to think seriously about it. The modulation reduction index forms the basis for the STI calculation. The modulation reduction caused by reverberation is taken into account separately, in the impulse response calculation, and the two effects are combined. This is confirmed in the original papers describing the STI, for instance Houtgast, Steeneken and Plomp, "Predicting speech intelligibility in rooms from the modulation transfer function. 1. General room acoustics", Acustica vol. 46, p. 60, 1980. Another good reference describing how it can be done using MLS is Rife, "Modulation transfer function measurement with maximum-length sequences", JAES vol. 40, p. 779, 1992. It should be noted that the method of measuring separately the modulation effects of reverberation and noise will not give correct results for systems where there is signal dependent noise, like codecs. In such cases the method described by Rife using a calibrated signal, no averaging and no truncation of the response should be used, and no correction as discussed above is necessary. This is possible with the current version of WinMLS, but will be made more convenient in the next version. The method of separate measurement can be handy, for instance when the correct speech and/or noise levels cannot be obtained at the time of measurement, or when it is of interest to simulate what changes in the levels will do to the STI value. Best wishes Johan L

	Subject STI Date Mon Jan 27 2003 10:02 Author Bernhard (bekamu@gmx.de)
I can reedout the STI value only with one decimal place after 0. How can I choose two decimal places like 0.65? I do not succed in getting the MTF values. In Room Acoustic Parameter Settings I activate the appropriate choice box but I cannot see any values. Thanks for your help.

Subject 2 decimals and MTF Date Sun Feb 2 2003 15:19 Author Lars Morset (morset@winmls.com)

Dear Bernhard, thanks for you question. >How can I choose two decimal places like 0.65? By using Calculate on the Room Acoustics menu. I assume you are looking at the plot of STI. The mark in this plot has only 1 decimal, and it should have been 2. This is fixed in the new version to be released. >I do not succed in getting the MTF values. In Room Acoustic >Parameter Settings I activate the appropriate choice box but >I cannot see any values. These choices apply to Room Acoustics->Calculate only. Try Calculate on the Room Acoustics menu. Best, Lars

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