Re: Optimal sweep duration for BRIR measurements (John Culling )

Subject: Re: Optimal sweep duration for BRIR measurements From: John Culling <CullingJ@xxxxxxxx> Date: Mon, 27 Jul 2015 15:10:06 +0000 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY> --_000_HE1PR02MB07486C2712F0D30541BA5E2E878E0HE1PR02MB0748eurp_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Dear list, I've had a number of helpful replies on and off the list that have helped a= good deal with clarifying things. The most significant point is the right method for establishing the level o= f noise. I was presuming that noise should be observable from the correlation between succ= essively taken impulse responses. Though this seems plausible, it led me to the impr= ession that there was less noise from shortish sweeps. In fact, one can measure the no= ise floor from a single impulse response, perhaps most elegantly by using Schroeder's revers= e integration method, for which there is a clear change in the function slope when the ta= il of the IR gives way to noise. Using this method, the benefit of longer sweeps become= s much more apparent. In a quiet office environment, the noise is about 50 dB down with= a 20 s sweep, whereas it is only about 35 dB down for a 2 s sweep. So the noise rejection= improves with sweep length, but is still pretty good even with a short one. Correlation a= lso has the problems that offsets in time can lead to a drop in value, which cannot eas= ily be compensated (cross-correlation will not help unless the delay is an integer number of s= ampling periods), and that one has to take more than one measurement to do the correlations. 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_HE1PR02MB07486C2712F0D30541BA5E2E878E0HE1PR02MB0748eurp_ 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 list,<o:p></o:p><= /span> <o:p> </o:p></spa= n> I've had a number of h= elpful replies on and off the list that have helped a good deal<o:p></o:p><= /span> with clarifying things= . <o:p></o:p> <o:p> </o:p></spa= n> The most significant p= oint is the right method for establishing the level of noise. I was<o:p></o= :p> presuming that noise s= hould be observable from the correlation between successively<o:p></o:p></s= pan> taken impulse response= s. Though this seems plausible, it led me to the impression that <o:p></o:p> there was less noise f= rom shortish sweeps.  In fact, one can measure the noise floor from a<= o:p></o:p> single impulse respons= e, perhaps most elegantly by using Schroeder's reverse integration<o:p></o:= p> method, for which ther= e is a clear change in the function slope when the tail of the IR<o:p></o:p= > gives way to noise. Us= ing this method,  the benefit of longer sweeps becomes much more<o:p><= /o:p> apparent. In a quiet o= ffice environment, the noise is about 50 dB down with a 20 s sweep,<o:p></o= :p> whereas it is only abo= ut 35 dB down for a 2 s sweep. So the noise rejection improves with<o:p></o= :p> sweep length, but is s= till pretty good even with a short one. Correlation also has the <o:p></o:p> problems that offsets = in time can lead to a drop in value, which cannot easily be compensated<o:p= ></o:p> (cross-correlation wil= l not help unless the delay is an integer number of sampling periods), <o:p></o:p> and that one has to ta= ke more than one measurement to do the correlations.<o:p></o:p> <o:p> </o:p></spa= n> John.<o:p></o:p></span= > <o:p> </o:p></spa= n> <o:p> </o:p></spa= n>  <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: +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, Prifysgol 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_HE1PR02MB07486C2712F0D30541BA5E2E878E0HE1PR02MB0748eurp_--

This message came from the mail archive
/var/www/postings/2015/
maintained by:

DAn Ellis <dpwe@ee.columbia.edu>
Electrical Engineering Dept., Columbia University