Optimal sweep duration for BRIR measurements (John Culling )

Subject: Optimal sweep duration for BRIR measurements From: John Culling <CullingJ@xxxxxxxx> Date: Fri, 24 Jul 2015 15:25:19 +0000 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY> --_000_HE1PR02MB074894A8FA23C7B083B8C28487810HE1PR02MB0748eurp_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Dear all, Basic Q... Does anyone have insight into the optimum sweep duration using Farina's met= hod for measuring room impulses responses? More detailed background... 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_HE1PR02MB074894A8FA23C7B083B8C28487810HE1PR02MB0748eurp_ Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable <html xmlns:v=3D"urn:schemas-microsoft-com:vml" xmlns:o=3D"urn:schemas-micr= osoft-com:office:office" xmlns:w=3D"urn:schemas-microsoft-com:office:word" = xmlns:m=3D"http://schemas.microsoft.com/office/2004/12/omml" xmlns=3D"http:= //www.w3.org/TR/REC-html40"> <head> <meta http-equiv=3D"Content-Type" content=3D"text/html; charset=3Diso-8859-= 1"> <meta name=3D"Generator" content=3D"Microsoft Word 15 (filtered medium)"> <style></style> </head> <body lang=3D"EN-GB" link=3D"#0563C1" vlink=3D"#954F72"> <div class=3D"WordSection1"> Dear all,<o:p></o:p> <o:p> </o:p> Basic Q…<o:p></o:p> <o:p> </o:p> Does anyone have insight into the optimum sweep dura= tion using Farina's method<o:p></o:p> for measuring room impulses responses?<o:p></o:p></p= > <o:p> </o:p> More detailed background…<o:p></o:p> <o:p> </o:p> We are planning to make an extensive series of measu= rements, and in preparation have<o:p></o:p> been testing the method using different sweep durati= ons. One way to check the method<o:p></o:p> is to correlate the impulses respones from repeated = measurements or those generated <o:p></o:p> with different durations.  To our surprise shor= t sweeps (1-2 seconds) appear to give more <o:p></o:p> reliable results (repeated sweeps correlate, r>0.= 98) than longer ones. Comparing sweeps<o:p></o:p> of different durations is a little trickier, because= we find a temporal offset that reduces<o:p></o:p> the correlation and can only be partially overcome b= y using cross-correlation. Nonetheless,<o:p></o:p> it is apparent that durations from 1 second upwards = correlate well, while going below one<o:p></o:p> second leads to reliable IRs, but ones that are inac= curate when compared with those from<o:p></o:p> longer sweep durations. <o:p></o:p> <o:p> </o:p> Our surprising conclusion is that ~2s should be fine= , but Farina refers to an ISO standard that <o:p></o:p> recommends very long sweeps (Farina has an example o= f 50s) to help overcome noise.<o:p></o:p> This seems an unintuitive rationale to us, since lon= ger sweeps should increase both the <o:p></o:p> signal energy captured and the noise energy, and the= method does not involve averaging<o:p></o:p> as far as I understand. Longer durations should help= address brief interupting sounds, but <o:p></o:p> I am unsure if that it what was the idea. In the pre= sence of continuous noise, we did not <o:p></o:p> notice any improvement in the IRs produced by longer= sweeps.<o:p></o:p> <o:p> </o:p> The nascent plan is to take >1 short sweep for ea= ch measurement and reject IRs that<o:p></o:p> that don't correlate well with another.<o:p></o:p></= p> <o:p> </o:p> Any insights/advice appreciated,<o:p></o:p> <o:p> </o:p> John.<o:p></o:p> <o:p> </o:p> <table class=3D"MsoNormalTable" border=3D"0" cellspacing=3D"0" cellpadding= =3D"0" style=3D"border-collapse:collapse"> <tbody> <tr> <td width=3D"301" valign=3D"top" style=3D"width:225.4pt;border:solid #BFBFB= F 1.0pt;border-right:solid windowtext 1.0pt;padding:0cm 5.4pt 0cm 5.4pt"> Prof. John Culling<o:p></o:p> School of Psychology,= Cardiff University<o:p></o:p> Tel: &#43= ;44 (0)29 2087 4556<o:p></o:p>= </td> <td width=3D"301" valign=3D"top" style=3D"width:225.4pt;border:solid #BFBFB= F 1.0pt;border-left:none;padding:0cm 5.4pt 0cm 5.4pt"> Yr Athro John Culling<o:p></o:p> Yr Ysgol Seicoleg, Pr= ifysgol Caerdydd <o:p></o:p> Ff=F4n : +44= (0)29 2087 4556<o:p></o:p> </td> </tr> </tbody> </table>  <o:p></o:p> <o:p> </o:p> </div> </body> </html> --_000_HE1PR02MB074894A8FA23C7B083B8C28487810HE1PR02MB0748eurp_--

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