Subject: Re: Optimal sweep duration for BRIR measurements From: Mendel Kleiner <mendel.kleiner@xxxxxxxx> Date: Mon, 27 Jul 2015 12:02:47 +0200 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>--Apple-Mail=_93ED0741-5F63-400E-A46A-36C4E0EC9F0D Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=windows-1252 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].=20 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 On 26 jul 2015, at 22:29, Philip Robinson <philrob22@xxxxxxxx> wrote: > 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. >=20 > Have you asked Farina? I'm sure he would be happy to advise. >=20 > Best,=20 > Philip >=20 > On 26 Jul 2015 10:46, "Neeraj Sharma" <neerajww@xxxxxxxx> 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 =3D 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)=20 > 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. >=20 > Best regards, > Neeks >=20 > On Sun, Jul 26, 2015 at 2:14 PM, Wenwu W. Wang <W.Wang@xxxxxxxx> = wrote: > Hi John, Dylan, >=20 > This is an interesting question. > Does this relate to the frequency used in the exponential sine sweep, = or the non-linear behaviour/distortion of the loudspeaker/sound card = used which may have different impacts on the short/long sweep signals? >=20 > Best wishes, > Wenwu >=20 >=20 >=20 > -- > Dr Wenwu Wang > Centre for Vision Speech and Signal Processing > Department of Electronic Engineering > University of Surrey > Guildford GU2 7XH > United Kingdom > Phone: +44 (0) 1483 686039 > Fax: +44 (0) 1483 686031 > Email: w.wang@xxxxxxxx > http://personal.ee.surrey.ac.uk/Personal/W.Wang/ >=20 > ________________________________________ > From: AUDITORY - Research in Auditory Perception = <AUDITORY@xxxxxxxx> on behalf of Menzies-Gow R.D. = <D.Menzies@xxxxxxxx> > Sent: 25 July 2015 11:43 > To: AUDITORY@xxxxxxxx > Subject: Re: Optimal sweep duration for BRIR measurements >=20 > Variations in measured BRIR could be due to anything changing in the = room =96 e.g. drafts, convection from heaters, people moving. Shorter = sweeps are less affected by this, but more effected by signal noise. = Could also be head movement if measuring live subjects. >=20 > Did you check the stability of the convolver by convolving the sweep = with the inverse? Could also try first convolving the sweep with a test = signal. >=20 >=20 >=20 > -- > Dylan Menzies > Senior Research Fellow > Institute of Sound and Vibration > University of Southampton, UK >=20 >=20 >=20 >=20 >=20 > On 24 July 2015 at 16:25, John Culling = <CullingJ@xxxxxxxx<mailto:CullingJ@xxxxxxxx>> wrote: > Dear all, >=20 > Basic Q=85 >=20 > Does anyone have insight into the optimum sweep duration using = Farina's method > for measuring room impulses responses? >=20 > More detailed background=85 >=20 > We are planning to make an extensive series of measurements, and in = preparation have > been testing the method using different sweep durations. One way to = check the method > is to correlate the impulses respones from repeated measurements or = those generated > with different durations. To our surprise short sweeps (1-2 seconds) = appear to give more > reliable results (repeated sweeps correlate, r>0.98) than longer ones. = Comparing sweeps > of different durations is a little trickier, because we find a = temporal offset that reduces > the correlation and can only be partially overcome by using = cross-correlation. Nonetheless, > it is apparent that durations from 1 second upwards correlate well, = while going below one > second leads to reliable IRs, but ones that are inaccurate when = compared with those from > longer sweep durations. >=20 > Our surprising conclusion is that ~2s should be fine, but Farina = refers to an ISO standard that > recommends very long sweeps (Farina has an example of 50s) to help = overcome noise. > This seems an unintuitive rationale to us, since longer sweeps should = increase both the > signal energy captured and the noise energy, and the method does not = involve averaging > as far as I understand. Longer durations should help address brief = interupting sounds, but > I am unsure if that it what was the idea. In the presence of = continuous noise, we did not > notice any improvement in the IRs produced by longer sweeps. >=20 > The nascent plan is to take >1 short sweep for each measurement and = reject IRs that > that don't correlate well with another. >=20 > Any insights/advice appreciated, >=20 > John. >=20 > Prof. John Culling > School of Psychology, Cardiff University > Tel: +44 (0)29 2087 4556<tel:%2B44%20%280%2929%202087%204556> >=20 > Yr Athro John Culling > Yr Ysgol Seicoleg, Prifysgol Caerdydd > Ff=F4n : +44 (0)29 2087 4556<tel:%2B44%20%280%2929%202087%204556> >=20 --Apple-Mail=_93ED0741-5F63-400E-A46A-36C4E0EC9F0D Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=windows-1252 <html><head><meta http-equiv=3D"Content-Type" content=3D"text/html = charset=3Dwindows-1252"><meta http-equiv=3D"Content-Type" = content=3D"text/html charset=3Dwindows-1252"></head><body = style=3D"word-wrap: break-word; -webkit-nbsp-mode: space; = -webkit-line-break: after-white-space;">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:<br><div><br>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]. </div><div><br></div><div>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].</div><div><br></div><div>Best = regards,</div><div><br></div><div>Mendel Kleiner<br><div><div>On 26 jul = 2015, at 22:29, Philip Robinson <<a = href=3D"mailto:philrob22@xxxxxxxx">philrob22@xxxxxxxx</a>> = wrote:</div><br class=3D"Apple-interchange-newline"><blockquote = type=3D"cite"><meta http-equiv=3D"Content-Type" content=3D"text/html; = charset=3Dutf-8"><p dir=3D"ltr">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. </p><p dir=3D"ltr">Have you asked Farina? I'm sure he would be = happy to advise. </p><p dir=3D"ltr">Best, <br> Philip</p> <div class=3D"gmail_quote">On 26 Jul 2015 10:46, "Neeraj Sharma" <<a = href=3D"mailto:neerajww@xxxxxxxx">neerajww@xxxxxxxx</a>> wrote:<br = type=3D"attribution"><blockquote class=3D"gmail_quote" style=3D"margin:0 = 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div = dir=3D"ltr"><div><div>I just did some RIR measurement in a varechoic = chamber. Interesting to find a discussion on it here. I use the = following specifications.<br>(Will be happy to know if there are = guidelines to be followed for proper RIR measurements, especially if a = database is to be released)<br></div>1. Linear (constant amplitude) sine = sweep (20-20 kHz)<br>2. Logarthim (constant amplitude) sine sweep = (20-20 kHz).<br></div>3. Sweep duration 20 sec, Fs =3D 48 = kHz<br><div><div>4. Ambient room noise of -50 dB (can be lowered a bit = more)<br></div><div>5. Microphones and speakers are at least 100 cm = above ground (to reduce low frequency dominance) <br>6. A small powerful = speaker. (the speaker is however not omnidirectional, and has no = separate HF and LF diaphragm)<br></div><div>7. Omni-directional mics = facing the speaker<br></div><div>8. Temperature of 25 degree = celsius<br></div><div>Remarks:<br></div><div>a. The RT60 with Linear and = Log sweep is quite close (difference within 100 msec).<br></div><div>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.</div><div>c. I will not consider smaller = duration sweep as an alternative to longer duration even under the = burden of computation.<br></div><div><br></div><div>Best = regards,<br></div><div>Neeks</div></div></div><div = class=3D"gmail_extra"><br><div class=3D"gmail_quote">On Sun, Jul 26, = 2015 at 2:14 PM, Wenwu W. Wang <span dir=3D"ltr"><<a = href=3D"mailto:W.Wang@xxxxxxxx" = target=3D"_blank">W.Wang@xxxxxxxx</a>></span> = wrote:<br><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 = .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi John, Dylan,<br> <br> This is an interesting question.<br> Does this relate to the frequency used in the exponential sine sweep, or = the non-linear behaviour/distortion of the loudspeaker/sound card used = which may have different impacts on the short/long sweep signals?<br> <br> Best wishes,<br> Wenwu<br> <br> <br> <br> --<br> Dr Wenwu Wang<br> Centre for Vision Speech and Signal Processing<br> Department of Electronic Engineering<br> University of Surrey<br> Guildford GU2 7XH<br> United Kingdom<br> Phone: <a href=3D"tel:%2B44%20%280%29%201483%20686039" = value=3D"+441483686039" target=3D"_blank">+44 (0) 1483 686039</a><br> Fax: <a href=3D"tel:%2B44%20%280%29%201483%20686031" = value=3D"+441483686031" target=3D"_blank">+44 (0) 1483 686031</a><br> Email: <a href=3D"mailto:w.wang@xxxxxxxx" = target=3D"_blank">w.wang@xxxxxxxx</a><br> <a href=3D"http://personal.ee.surrey.ac.uk/Personal/W.Wang/" = rel=3D"noreferrer" = target=3D"_blank">http://personal.ee.surrey.ac.uk/Personal/W.Wang/</a><br>= <br> ________________________________________<br> From: AUDITORY - Research in Auditory Perception <<a = href=3D"mailto:AUDITORY@xxxxxxxx" = target=3D"_blank">AUDITORY@xxxxxxxx</a>> on behalf of = Menzies-Gow R.D. <<a href=3D"mailto:D.Menzies@xxxxxxxx" = target=3D"_blank">D.Menzies@xxxxxxxx</a>><br> Sent: 25 July 2015 11:43<br> To: <a href=3D"mailto:AUDITORY@xxxxxxxx" = target=3D"_blank">AUDITORY@xxxxxxxx</a><br> Subject: Re: Optimal sweep duration for BRIR measurements<br> <div><br> Variations in measured BRIR could be due to anything changing in the = room =96 e.g. drafts, convection from heaters, people moving. Shorter = sweeps are less affected by this, but more effected by signal noise. = Could also be head movement if measuring live subjects.<br> <br> Did you check the stability of the convolver by convolving the sweep = with the inverse? Could also try first convolving the sweep with a test = signal.<br> <br> <br> <br> --<br> Dylan Menzies<br> Senior Research Fellow<br> Institute of Sound and Vibration<br> University of Southampton, UK<br> <br> <br> <br> <br> <br> On 24 July 2015 at 16:25, John Culling <<a = href=3D"mailto:CullingJ@xxxxxxxx" = target=3D"_blank">CullingJ@xxxxxxxx</a><mailto:<a = href=3D"mailto:CullingJ@xxxxxxxx" = target=3D"_blank">CullingJ@xxxxxxxx</a>>> wrote:<br> Dear all,<br> <br> Basic Q=85<br> <br> Does anyone have insight into the optimum sweep duration using Farina's = method<br> for measuring room impulses responses?<br> <br> More detailed background=85<br> <br> We are planning to make an extensive series of measurements, and in = preparation have<br> been testing the method using different sweep durations. One way to = check the method<br> is to correlate the impulses respones from repeated measurements or = those generated<br> with different durations. To our surprise short sweeps (1-2 = seconds) appear to give more<br> reliable results (repeated sweeps correlate, r>0.98) than longer = ones. Comparing sweeps<br> of different durations is a little trickier, because we find a temporal = offset that reduces<br> the correlation and can only be partially overcome by using = cross-correlation. Nonetheless,<br> it is apparent that durations from 1 second upwards correlate well, = while going below one<br> second leads to reliable IRs, but ones that are inaccurate when compared = with those from<br> longer sweep durations.<br> <br> Our surprising conclusion is that ~2s should be fine, but Farina refers = to an ISO standard that<br> recommends very long sweeps (Farina has an example of 50s) to help = overcome noise.<br> This seems an unintuitive rationale to us, since longer sweeps should = increase both the<br> signal energy captured and the noise energy, and the method does not = involve averaging<br> as far as I understand. Longer durations should help address brief = interupting sounds, but<br> I am unsure if that it what was the idea. In the presence of continuous = noise, we did not<br> notice any improvement in the IRs produced by longer sweeps.<br> <br> The nascent plan is to take >1 short sweep for each measurement and = reject IRs that<br> that don't correlate well with another.<br> <br> Any insights/advice appreciated,<br> <br> John.<br> <br> Prof. John Culling<br> School of Psychology, Cardiff University<br> Tel: <a href=3D"tel:%2B44%20%280%2929%202087%204556" = value=3D"+442920874556" target=3D"_blank">+44 (0)29 2087 = 4556</a><tel:%2B44%20%280%2929%202087%204556><br> <br> Yr Athro John Culling<br> Yr Ysgol Seicoleg, Prifysgol Caerdydd<br> Ff=F4n : <a href=3D"tel:%2B44%20%280%2929%202087%204556" = value=3D"+442920874556" target=3D"_blank">+44 (0)29 2087 = 4556</a><tel:%2B44%20%280%2929%202087%204556><br> </div></blockquote></div><br></div> </blockquote></div> </blockquote></div><br></div></body></html>= --Apple-Mail=_93ED0741-5F63-400E-A46A-36C4E0EC9F0D--