Filter design with 'freqsamp' method?
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From: Pete Fraser on 2 Jul 2010 19:55 Steve Pope wrote: > A good thing to remember is that any filter that is as > selective as a given Butterworth filter will have a > similar RMS delay spread as the Butterworth filter. > So no free lunch on phase issues in many cases. Pete Fraser replied: >But I'm doing a symmetric FIR with the Butterworth >amplitude response. Then robert bristow-johnson said: > so then you'll get even *more* phase shift delay. (Butterworths are > minimum phase and linear phase is not minimum phase unless it's a wire > or a simple gain.) True, but Steve and I were talking about RMS delay spread. Pete
From: robert bristow-johnson on 2 Jul 2010 23:37 On Jul 2, 7:55 pm, "Pete Fraser" <pfra...(a)covad.net> wrote: > > ... but Steve and I were talking about RMS delay spread. > "spread" from what? zero? or some mean delay? how is the mean defined? "RMS delay spread" hasn't been a parameter i've been familiar with. is it a measure of overall phase nonlinearity? just curious. r b-j
From: Steve Pope on 2 Jul 2010 23:52 robert bristow-johnson <rbj(a)audioimagination.com> wrote: >On Jul 2, 7:55�pm, "Pete Fraser" <pfra...(a)covad.net> wrote: >> ... but Steve and I were talking about RMS delay spread. >"spread" from what? zero? or some mean delay? how is the mean >defined? >"RMS delay spread" hasn't been a parameter i've been familiar with. >just curious. Interestingly some of the literature defintions of RMS delay spread I disagree with, but it basically goes something like this: if the impulse response is: (sum over i) (h(i) * (t - tau(i))) then the average delay is ave = (sum over i)(h(i)*tau(i) / (sum over i)(h(i)) and the RMS delay spread is sqrt((sum over i)(h(i)*((tau(i) - ave)^2)). >is it a measure of overall phase nonlinearity? No, the phase can be linear but you can have a large RMS delay spread. I'm interested if anyone doesn't like the expression I just gave above. I've seen expressions that were not equivalent to this (I'm going to say by Spencer). Steve
From: Steve Pope on 2 Jul 2010 23:58 Oops, let me fix this. I left out some absolute values. the impulse response is: (sum over i) (h(i) * (t - tau(i))) then the average delay is ave = (sum over i)(abs(h(i))*tau(i) / (sum over i)(abs(h(i))) and the RMS delay spread is sqrt((sum over i)(abs(h(i))*((tau(i) - ave)^2)). S.
From: Greg Berchin on 3 Jul 2010 06:48
On Fri, 2 Jul 2010 20:37:14 -0700 (PDT), robert bristow-johnson <rbj(a)audioimagination.com> wrote: >> ... but Steve and I were talking about RMS delay spread. >> > >"spread" from what? zero? or some mean delay? how is the mean >defined? > >"RMS delay spread" hasn't been a parameter i've been familiar with. >is it a measure of overall phase nonlinearity? Possibly useful: see US Patent 5375067 for a discussion of Central Time and RMS Delay. Greg |