Filter design with 'freqsamp' method?
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From: Greg Berchin on 3 Jul 2010 15:29 On Sat, 3 Jul 2010 11:34:44 -0700 (PDT), robert bristow-johnson <rbj(a)audioimagination.com> wrote: >well, i'm still trying to pin these guys down. if their r.m.s. delay >parameter ("spread" or whatever it's called) is a measure of deviation >from phase linearity, then nothing can beat a phase linear FIR. but >if it's a measure of phase delay or group delay (from zero), then a >minimum-phase filter will beat linear-phase. This concept of "delay spread" does seem rather ambiguous. If it's related to phase delay, then as you say nothing beats minimum-phase and that will be reflected in the Central Time and RMS Duration. If it's related to group delay, then it's an even more difficult-to-grasp concept than group delay itself -- I suppose it would be a measurement of the variation in delay in the envelopes of signals that occupy bandwidths that are "narrow but not too narrow", as a function of the centers of the narrow bands that they occupy. Or something like that. Greg
From: Greg Berchin on 3 Jul 2010 15:33 On Sat, 3 Jul 2010 11:34:44 -0700 (PDT), robert bristow-johnson <rbj(a)audioimagination.com> wrote: >Greg, i didn't know about this patent of yours. good show! Thanks. You know what really bugs me about that patent? I wrote the patent myself, though it was of course blessed by the patent attorney. Now, sixteen years later, I'm not sure that I even understand it any more. Greg
From: Fred Marshall on 3 Jul 2010 18:21 robert bristow-johnson wrote: > On Jul 1, 10:59 am, Fred Marshall <fmarshallx(a)remove_the_xacm.org> > wrote: >> r b-j, >> >> Well, maybe I've had it wrong all these years but I'd say that the >> windowing method starts with N frequency samples where N is the length >> of the filter you want. > > so then, since the DFT and iDFT are bijective (i love using fancy- > pants words), why window? if h[n] has N samples and N degrees of > freedom, so does H[k]. you specify your N frequency samples and you > can hit it perfectly with no windowing. > > so, that seems curious to me. > > r b-j You window because the frequency response between those points can be nasty. Either you don't window and convolve those samples with a matching sinc er.. Dirichlet or you window and convolve those samples with something else. The trade is that the Dirichlet matches all the samples exactly. Other windows don't. Some match them all except the adjacent two as in the 1/2 1 1/2 sum of adjacent Dirichlets. It still has zeros in the sum at all the other sample points - so the convolution doesn't perturb their values. And, the values between points are better behaved. And making N larger to begin with doesn't affect any of this in my way of looking at it. Fred
From: Steve Pope on 4 Jul 2010 12:15 Pete Fraser <pfraser(a)covad.net> wrote: >"robert bristow-johnson" <rbj(a)audioimagination.com> wrote in message >> well, i'm still trying to pin these guys down. if their r.m.s. delay >> parameter ("spread" or whatever it's called) is a measure of deviation >> from phase linearity, then nothing can beat a phase linear FIR. >I don't know if there's a formal definition. >I just assumed it was a measure of the dispersiveness >(frequency dependent delay) of the filter. So as to save you guys some googling I have uploaded Ibnkahla's definition of RMS delay spread to the following link which I will leave in place for a few days. Hopefully this makes things less ambiguous. http://www.rahul.net/spp/IbnkahlaDelaySpread.bmp Steve
From: Greg Berchin on 4 Jul 2010 13:35
On Sun, 4 Jul 2010 16:15:35 +0000 (UTC), spope33(a)speedymail.org (Steve Pope) wrote: >So as to save you guys some googling I have uploaded Ibnkahla's >definition of RMS delay spread to the following link which >I will leave in place for a few days. > >Hopefully this makes things less ambiguous. > >http://www.rahul.net/spp/IbnkahlaDelaySpread.bmp I only gave it a cursory look, but comparing that with the discussion of moments that I put into US Patent 5375067, Ibnkahla's definition of RMS delay spread appears to be the same as RMS Duration. Greg |