Subject: Re: swept sine accuracy From: Jose Almagro <luegotelodigo@xxxxxxxx> Date: Fri, 6 Mar 2009 11:49:12 +0100 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>--001636e1fb0a0e06c204647109f2 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable I agree that the main problem is SNR/INR, anyway there's a comparison between short sweeps average and long sweeps I think it's written by Farina but I'm not sure, maybe by M=FCller. Best regards 2009/3/6 Piotr Majdak <piotr@xxxxxxxx> > Dear James, > > If you have noise in the system (=3Droom) then the sweep duration primarl= y > depends on the signal-to-noise ratio (SNR) you want to achieve. This is > because usually, the maximum amplitude of the loudspeaker is limited. > Further, for exponential sweeps, the SNR may depend on frequency, f.e., i= t's > pink if noise is white. > > For example, we use sweeps with at least 1.5-s duration for measurements = in > a sound chamber (18 dB noise) to achieve an SNR of 60 dB. For such long > sweeps, the frequency smearing is negligible. > > However, I do not have a theoretical result... > > br, Piotr Majdak > > > James W. Beauchamp wrote: > >> Guys, >> >> This is a not strictly an auditory question, but it could be >> useful for people doing acoustic measurements. If you use a >> swept sine wave to measure the frequency response of a linear >> system, what is the limitation on the speed of the sweep in >> terms of how accurate the result would be? I imagine it has >> something to do with how smooth the actual frequency response is. If it >> has some pronounced bumps, they could be smoothed >> out if the sweep is too fast. >> >> In practice, you could sweep at some arbitrary rate, and then >> slow it by a factor of two, and if the result is the same >> (within an acceptable tolerance) you could say that you've >> converged on the solution. >> >> But I'd like to have a theoretical result. >> >> Jim Beauchamp >> Univ. of Illinois at Urbana-Champaign >> >> > --001636e1fb0a0e06c204647109f2 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable <div>=A0=A0=A0 I agree that the main problem is SNR/INR, anyway there's= a comparison between short sweeps average and long sweeps I think it's= written by Farina but I'm not sure, maybe by M=FCller.</div> <div>=A0</div> <div>=A0=A0=A0 Best regards<br><br></div> <div class=3D"gmail_quote">2009/3/6 Piotr Majdak <span dir=3D"ltr"><<a h= ref=3D"mailto:piotr@xxxxxxxx">piotr@xxxxxxxx</a>></span><br> <blockquote class=3D"gmail_quote" style=3D"PADDING-LEFT: 1ex; MARGIN: 0px 0= px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">Dear James,<br><br>If you have n= oise in the system (=3Droom) then the sweep duration primarly depends on th= e signal-to-noise ratio (SNR) you want to achieve. This is because usually,= the maximum amplitude of the loudspeaker is limited. Further, for exponent= ial sweeps, the SNR may depend on frequency, f.e., it's pink if noise i= s white.<br> <br>For example, we use sweeps with at least 1.5-s duration for measurement= s in a sound chamber (18 dB noise) to achieve an SNR of 60 dB. For such lon= g sweeps, the frequency smearing is negligible.<br><br>However, I do not ha= ve a theoretical result...<br> <br>br, Piotr Majdak=20 <div> <div></div> <div class=3D"h5"><br><br>James W. Beauchamp wrote:<br> <blockquote class=3D"gmail_quote" style=3D"PADDING-LEFT: 1ex; MARGIN: 0px 0= px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">Guys,<br><br>This is a not stric= tly an auditory question, but it could be<br>useful for people doing acoust= ic measurements. If you use a<br> swept sine wave to measure the frequency response of a linear<br>system, wh= at is the limitation on the speed of the sweep in<br>terms of how accurate = the result would be? I imagine it has<br>something to do with how smooth th= e actual frequency response is. If it has some pronounced bumps, they could= be smoothed<br> out if the sweep is too fast.<br><br>In practice, you could sweep at some a= rbitrary rate, and then<br>slow it by a factor of two, and if the result is= the same<br>(within an acceptable tolerance) you could say that you've= <br> converged on the solution.<br><br>But I'd like to have a theoretical re= sult.<br><br>Jim Beauchamp<br>Univ. of Illinois at Urbana-Champaign<br>=A0<= br></blockquote></div></div></blockquote></div><br> --001636e1fb0a0e06c204647109f2--