> It turns out that whatever the value is for m, you will have n zeros > spaced at equal intervals around the unit circle for the mean filter
I had that intuition, thanks for clarifying it should be easy to convert from cpoles and czeros to biquad, I'll get to it soon. cheers 2015-09-08 18:07 GMT-03:00 David Medine <[email protected]>: > I'm not sure how to do it with biquads, but I'm sure it's possible. It is > absolutley possible to design an IIR filter that approximates this and then > build it out of biquad sections, but I would have to look long and hard at > my DSP theory texts to figure it out. > > I *do* know how to do it with [czero~] objects, though. The difference > equation for a mean across m samples is: > > y(n) = 1/m * (x(n) + x(n-1) + ... + x(n-m+1)) > > so the z-transform is: > > h(z) = 1/m * (1+ z^(m-1) + z^(m-2) + ... + z) > > This is a polynomial in z and the roots of this polynomial (which are > complex) are the locations of the zeros. I'm bad at algebra, so I used > octave (the function is called roots) to find the roots. It turns out that > whatever the value is for m, you will have n zeros spaced at equal > intervals around the unit circle for the mean filter *except* for an > absent zero at 1 (m-1 zeros in all). So for an m=8, your zeros would be at > [.707, .707] [0,1] [ -.707, .707] [-1, 0] etc. I attach the pole-zero plot > of the filter for m=8. > > Your biquad-based solution to the 4 point average is very clever. It is > very challenging (for me anyway) to generalize this filter design problem > with biquads, so I have something to think about when I'm on the bus for a > little while. If I come up with anything I'll post it. > > Cheers, > David > > > On 9/7/2015 9:00 PM, Alexandre Torres Porres wrote: > > Hi, I was able to implement a 4 point average filter with raw filters and > biquad~ in Pd (find attached patch). I'm struggling to finda a way to > implement an 8 point average filter with biquads~ and raw filters... > Anyone can help? > > thanks > > > > > _______________________________________________pd-l...@lists.iem.at mailing > list > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list > > > > _______________________________________________ > [email protected] mailing list > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list > >
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