Subject: Re: Optimal sweep duration for BRIR measurements From: Philip Robinson <philrob22@xxxxxxxx> Date: Sun, 26 Jul 2015 21:29:05 +0100 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>--047d7b5d68c6a9d397051bcd163b Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable 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@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) > 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 affec= t > the RIR, and RT60. Hence, it is important to be sure that no harmonics ar= e > 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 > > On Sun, Jul 26, 2015 at 2:14 PM, Wenwu W. Wang <W.Wang@xxxxxxxx> > wrote: > >> Hi John, Dylan, >> >> 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? >> >> Best wishes, >> Wenwu >> >> >> >> -- >> 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/ >> >> ________________________________________ >> 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 >> >> Variations in measured BRIR could be due to anything changing in the roo= m >> =E2=80=93 e.g. drafts, convection from heaters, people moving. Shorter s= weeps are >> less affected by this, but more effected by signal noise. Could also be >> head movement if measuring live subjects. >> >> Did you check the stability of the convolver by convolving the sweep wit= h >> the inverse? Could also try first convolving the sweep with a test signa= l. >> >> >> >> -- >> Dylan Menzies >> Senior Research Fellow >> Institute of Sound and Vibration >> University of Southampton, UK >> >> >> >> >> >> On 24 July 2015 at 16:25, John Culling <CullingJ@xxxxxxxx<mailto: >> CullingJ@xxxxxxxx>> wrote: >> Dear all, >> >> Basic Q=E2=80=A6 >> >> Does anyone have insight into the optimum sweep duration using Farina's >> method >> for measuring room impulses responses? >> >> More detailed background=E2=80=A6 >> >> 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 chec= k >> the method >> is to correlate the impulses respones from repeated measurements or thos= e >> 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, whil= e >> going below one >> second leads to reliable IRs, but ones that are inaccurate when compared >> with those from >> longer sweep durations. >> >> 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. >> >> The nascent plan is to take >1 short sweep for each measurement and >> reject IRs that >> that don't correlate well with another. >> >> Any insights/advice appreciated, >> >> John. >> >> Prof. John Culling >> School of Psychology, Cardiff University >> Tel: +44 (0)29 2087 4556<tel:%2B44%20%280%2929%202087%204556> >> >> Yr Athro John Culling >> Yr Ysgol Seicoleg, Prifysgol Caerdydd >> Ff=C3=B4n : +44 (0)29 2087 4556<tel:%2B44%20%280%2929%202087%204556> >> > > --047d7b5d68c6a9d397051bcd163b Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable <p dir=3D"ltr">Perhaps it's obvious, but I have to mention it because n= o one else has. The sweep should be longer than the response that is being = measured.=C2=A0 For a room,=C2=A0 one second is pretty short.=C2=A0 For an = HRTF,=C2=A0 probably ok. For concert halls we often use 4-8 seconds,=C2=A0 = which gives good signal to noise ratios, but is not so long that the likeli= hood of an interupting noise becomes high. </p> <p dir=3D"ltr">Have you asked Farina? I'm sure he would be happy to adv= ise. </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"><d= iv><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>(W= ill 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. Linea= r (constant amplitude) sine sweep (20-20 kHz)<br>2. Logarthim (constant am= plitude) 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 m= ore)<br></div><div>5. Microphones and speakers are at least 100 cm above gr= ound (to reduce low frequency dominance) <br>6. A small powerful speaker. (= the speaker is however not omnidirectional, and has no separate HF and LF d= iaphragm)<br></div><div>7. Omni-directional mics facing the speaker<br></di= v><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 withi= n 100 msec).<br></div><div>b. Peak speaker volume results in harmonics of t= he 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 cons= ider 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.Wan= g@xxxxxxxx</a>></span> wrote:<br><blockquote class=3D"gmail_quote" s= tyle=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi J= ohn, Dylan,<br> <br> This is an interesting question.<br> Does this relate to the frequency used in the exponential sine sweep, or th= e 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"+4414836860= 39" 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= ey.ac.uk</a><br> <a href=3D"http://personal.ee.surrey.ac.uk/Personal/W.Wang/" rel=3D"norefer= rer" 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:AUDI= TORY@xxxxxxxx" target=3D"_blank">AUDITORY@xxxxxxxx</a>> on= behalf of Menzies-Gow R.D. <<a href=3D"mailto:D.Menzies@xxxxxxxx" ta= rget=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= LISTS.MCGILL.CA</a><br> Subject: Re: Optimal sweep duration for BRIR measurements<br> <div><div><br> Variations in measured BRIR could be due to anything changing in the room = =E2=80=93 e.g. drafts, convection from heaters, people moving. Shorter swee= ps 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 t= he inverse? Could also try first convolving the sweep with a test signal.<b= r> <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= ff.ac.uk" 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=E2=80=A6<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=E2=80=A6<br> <br> We are planning to make an extensive series of measurements, and in prepara= tion have<br> been testing the method using different sweep durations. One way to check t= he method<br> is to correlate the impulses respones from repeated measurements or those g= enerated<br> with different durations.=C2=A0 To our surprise short sweeps (1-2 seconds) = appear to give more<br> reliable results (repeated sweeps correlate, r>0.98) than longer ones. C= omparing sweeps<br> of different durations is a little trickier, because we find a temporal off= set that reduces<br> the correlation and can only be partially overcome by using cross-correlati= on. Nonetheless,<br> it is apparent that durations from 1 second upwards correlate well, while g= oing below one<br> second leads to reliable IRs, but ones that are inaccurate when compared wi= th 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 incre= ase both the<br> signal energy captured and the noise energy, and the method does not involv= e averaging<br> as far as I understand. Longer durations should help address brief interupt= ing sounds, but<br> I am unsure if that it what was the idea. In the presence of continuous noi= se, 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 reje= ct 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=C3=B4n : <a href=3D"tel:%2B44%20%280%2929%202087%204556" value=3D"+44292= 0874556" target=3D"_blank">+44 (0)29 2087 4556</a><tel:%2B44%20%280%2929= %202087%204556><br> </div></div></blockquote></div><br></div> </blockquote></div> --047d7b5d68c6a9d397051bcd163b--