[PD] 8 point average filter with biquad and raw filters?

[Alexandre Torres Porres]

>  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 <dmedine at ucsd.edu>:

> 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
>
>
>
>
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