Re: Optimal sweep duration for BRIR measurements ("Richard F. Lyon" )

Subject: Re: Optimal sweep duration for BRIR measurements From: "Richard F. Lyon" <dicklyon@xxxxxxxx> Date: Fri, 24 Jul 2015 22:34:26 -0700 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY> --001a113ff1e8413db4051bac7949 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable If the procedure with long sweeps involves an FFT of the whole long signal, then that's a problem. On the other hand, if you use more local processing, then longer sweeps should get you more reliable information and more noise averaging. Published methods are often the former. With more work, you can make long sweeps pay off better. But maybe you don't need to go that far. Dick On Fri, Jul 24, 2015 at 8:25 AM, John Culling <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 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. > > > > Our surprising conclusion is that ~2s should be fine, but Farina refers t= o > 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 rejec= t > 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 > > Yr Athro John Culling > > Yr Ysgol Seicoleg, Prifysgol Caerdydd > > Ff=C3=B4n : +44 (0)29 2087 4556 > > > > > --001a113ff1e8413db4051bac7949 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable <div dir=3D"ltr"><div><div><div><div>If the procedure with long sweeps invo= lves an FFT of the whole long signal, then that's a problem. </div>O= n the other hand, if you use more local processing, then longer sweeps shou= ld get you more reliable information and more noise averaging. </div>Pub= lished methods are often the former.=C2=A0 With more work, you can make lon= g sweeps pay off better. </div>But maybe you don't need to go that f= ar. </div>Dick </div><div class=3D"gmail_extra"> <div clas= s=3D"gmail_quote">On Fri, Jul 24, 2015 at 8:25 AM, John Culling <<a href=3D"mailto:CullingJ@xxxxxxxx" target=3D"_blank">Cu= llingJ@xxxxxxxx</a>> wrote: <blockquote class=3D"gmail_qu= ote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex= "> <div link=3D"#0563C1" vlink=3D"#954F72" lang=3D"EN-GB"> <div> Dear all, =C2=A0 Basic Q=E2=80=A6 =C2=A0 Does anyone have insight into the optimum sweep dura= tion using Farina's method for measuring room impulses responses?= =C2=A0 More detailed background=E2=80=A6 =C2=A0 We are planning to make an extensive series of measu= rements, and in preparation have been testing the method using different sweep durati= ons. One way to check the method is to correlate the impulses respones from repeated = measurements or those generated with different durations.=C2=A0 To our surprise shor= t 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 b= y 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 inac= curate when compared with those from longer sweep durations. =C2=A0 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 o= f 50s) to help overcome noise. This seems an unintuitive rationale to us, since lon= ger 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 pre= sence of continuous noise, we did not notice any improvement in the IRs produced by longer= sweeps. =C2=A0 The nascent plan is to take >1 short sweep for ea= ch measurement and reject IRs that that don't correlate well with another.<u= > =C2=A0 Any insights/advice appreciated, =C2=A0 John. =C2=A0 <table style=3D"border-collapse:collapse" border=3D"0" cellpadding=3D"0" ce= llspacing=3D"0"> <tbody> <tr> <td style=3D"width:225.4pt;border:solid #bfbfbf 1.0pt;border-right:solid wi= ndowtext 1.0pt;padding:0cm 5.4pt 0cm 5.4pt" valign=3D"top" width=3D"301"> Prof. John Culling School of Psychology, Cardiff University<= u> Tel: <a href=3D"tel:%2B44%20%280%292= 9%202087%204556" value=3D"+442920874556" target=3D"_blank">+44 (0)29 2087 4= 556</a> </td> <td style=3D"width:225.4pt;border:solid #bfbfbf 1.0pt;border-left:none;padd= ing:0cm 5.4pt 0cm 5.4pt" valign=3D"top" width=3D"301"> Yr Athro John Culling Yr Ysgol Seicoleg, Prifysgol Caerdydd Ff=C3=B4n=C2=A0: <a href=3D"tel:%2B44%20%280%292= 9%202087%204556" value=3D"+442920874556" target=3D"_blank">+44 (0)29 2087 4= 556</a> </td> </tr> </tbody> </table> =C2=A0 =C2=A0 </div> </div> </blockquote></div> </div> --001a113ff1e8413db4051bac7949--

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