Re: [Audacity-nyquist] Filtering with arbitrary a, b coeff. in Nyquist (Mikael Ogren)

[Roger D. <rb...@cs...>]

I assume your "a" and "b" coefficients are the terms for an IIR filter. 
Nyquist does not have a built-in function for arbitrary IIR filters. You 
can combine biquad filters, and you can do convolution for an arbitrary 
FIR filter. I'm not sure how to reduce a set of IIR coefficients to a 
series of biquad filters. I don't think it would be too hard to add a 
general IIR filter (probably not time-varying) to Nyquist's collection, 
or if someone wants to write it, I'll incorporate it.

Audacity works on a longer time cycle and doesn't automatically pick up 
the latest version of Nyquist -- we're not completely in sync on source 
code control, cross-platform support, and it's a big testing job -- so 
getting the filter into Nyquist is just the first step.

Another possibility is to implement the filter in Lisp. It will be 100 
times slower than C, but maybe that's tolerable.

-Roger