From: Roger Dannenberg <rbd@cs...>  20061020 20:29:29

I assume your "a" and "b" coefficients are the terms for an IIR filter. Nyquist does not have a builtin 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 timevarying) 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, crossplatform 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 