Re: Optimal sweep duration for BRIR measurements (Anders Tornvig Christensen )

Subject: Re: Optimal sweep duration for BRIR measurements From: Anders Tornvig Christensen <atc@xxxxxxxx> Date: Mon, 27 Jul 2015 07:07:23 +0000 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY> --_000_2DC307A9A8F2AA4F9051AD6874B268B5987FFA3CADEXCHMBX21aaud_ Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable Hello John, The sweep method at a single frequency is an approximation to a steady-stat= e measurement with a pure tone. Longer sweeps give higher signal to noise r= atio per sweep because it spends more time per frequency. Short repeated sweeps (but not shorter than the length of the impulse respo= nse) are good, if time-varying or sudden noise that doesn't average out is = likely to contaminate the measurement. Sweep duration (and "rate" in general) also matters if the system (room in = your case) is nonlinear, time-variant, or both, but that's another discussi= on. Something is wrong with your implementation if the temporal offset of the i= mpulse responses you measure depends on the sweep duration. You should be a= ble to check this by connecting the output of your sound card directly to i= ts input. Also note that wrongly measured or wrongly computed impulse respo= nses may be very reproducible in terms of correlation. Best, Anders PhD student in acoustics Aalborg University, Denmark ________________________________ From: AUDITORY - Research in Auditory Perception [AUDITORY@xxxxxxxx= on behalf of John Culling [CullingJ@xxxxxxxx Sent: Friday, July 24, 2015 5:25 PM To: AUDITORY@xxxxxxxx Subject: Optimal sweep duration for BRIR measurements Dear all, Basic Q=85 Does anyone have insight into the optimum sweep duration using Farina's met= hod for measuring room impulses responses? More detailed background=85 We are planning to make an extensive series of measurements, and in prepara= tion have been testing the method using different sweep durations. One way to check t= he method is to correlate the impulses respones from repeated measurements or those g= enerated with different durations. To our surprise short sweeps (1-2 seconds) appea= r to give more reliable results (repeated sweeps correlate, r>0.98) than longer ones. Comp= aring sweeps of different durations is a little trickier, because we find a temporal off= set that reduces the correlation and can only be partially overcome by using cross-correlati= on. Nonetheless, it is apparent that durations from 1 second upwards correlate well, while g= oing below one second leads to reliable IRs, but ones that are inaccurate when compared wi= th 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 incre= ase both the signal energy captured and the noise energy, and the method does not involv= e averaging as far as I understand. Longer durations should help address brief interupt= ing sounds, but I am unsure if that it what was the idea. In the presence of continuous noi= se, 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 Yr Athro John Culling Yr Ysgol Seicoleg, Prifysgol Caerdydd Ff=F4n : +44 (0)29 2087 4556 --_000_2DC307A9A8F2AA4F9051AD6874B268B5987FFA3CADEXCHMBX21aaud_ Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable <html dir=3D"ltr"> <head> <meta http-equiv=3D"Content-Type" content=3D"text/html; charset=3DWindows-1= 252"> <style>=0A= =0A= </style><style id=3D"owaParaStyle" type=3D"text/css">=0A= =0A= P {margin-top:0;margin-bottom:0;}</style> </head> <body ocsi=3D"0" fpstyle=3D"1" lang=3D"EN-GB" link=3D"#0563C1" vlink=3D"#95= 4F72"> <div style=3D"direction: ltr;font-family: Tahoma;color: #000000;font-size: = 10pt;"> <div style=3D"direction:ltr; font-family:Tahoma; color:#000000; font-size:1= 0pt">Hello John, The sweep method at a single frequency is an approximation to a steady-stat= e measurement with a pure tone. Longer sweeps give higher signal to noise r= atio per sweep because it spends more time per frequency. Short repeated sweeps (but not shorter than the length of the impulse respo= nse) are good, if time-varying or sudden noise that doesn't average out is = likely to contaminate the measurement. Sweep duration (and "rate" in general) also matters if the system= (room in your case) is nonlinear, time-variant, or both, but that's anothe= r discussion. Something is wrong with your implementation if the temporal offset of the i= mpulse responses you measure depends on the sweep duration. You should be a= ble to check this by connecting the output of your sound card directly to i= ts input. Also note that wrongly measured or wrongly computed impulse responses may be very reproducible in= terms of correlation. Best, Anders PhD student in acoustics Aalborg University, Denmark <div style=3D"font-family:Times New Roman; color:#000000; font-size:16px"> <hr tabindex=3D"-1"> <div id=3D"divRpF437927" style=3D"direction:ltr">From: AUDITORY - Research in Auditory Perce= ption [AUDITORY@xxxxxxxx on behalf of John Culling [CullingJ@xxxxxxxx= F.AC.UK] Sent: Friday, July 24, 2015 5:25 PM To: AUDITORY@xxxxxxxx Subject: Optimal sweep duration for BRIR measurements </div> <div></div> <div> <div class=3D"WordSection1"> Dear all,   Basic Q=85   Does anyone have insight into the optimum sweep dura= tion using Farina's method for measuring room impulses responses?   More detailed background=85   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.  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.   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.   The nascent plan is to take >1 short sweep for ea= ch measurement and reject IRs that that don't correlate well with another.   Any insights/advice appreciated,   John.   <table class=3D"MsoNormalTable" style=3D"border-collapse:collapse" border= =3D"0" cellpadding=3D"0" cellspacing=3D"0"> <tbody> <tr> <td style=3D"width:225.4pt; border:solid #BFBFBF 1.0pt; border-right:solid = windowtext 1.0pt; padding:0cm 5.4pt 0cm 5.4pt" valign=3D"top" width=3D"301"= > Prof. John Culling School of Psychology, Cardiff University= Tel: +44 (0)29 2087 4556= </td> <td style=3D"width:225.4pt; border:solid #BFBFBF 1.0pt; border-left:none; p= adding:0cm 5.4pt 0cm 5.4pt" valign=3D"top" width=3D"301"> Yr Athro John Culling Yr Ysgol Seicoleg, Prifysgol Caerdydd Ff=F4n : +44 (0)29 2087 4556</p= > </td> </tr> </tbody> </table>     </div> </div> </div> </div> </div> </body> </html> --_000_2DC307A9A8F2AA4F9051AD6874B268B5987FFA3CADEXCHMBX21aaud_--

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