kofron/KDSP.jl — pull request #1 by simonster (2012-12-06 03:06:33+00:00)
Title: Beginnings of filter design module

Transformation between prototype filters and lowpass, highpass, bandpass, and bandstop filters is implemented. Currently, only a Butterworth prototype is available. I make no guarantees with regard to the accuracy or numerical stability of the algorithms used.

The interface looks like:

```julia
analogfilter(Bandpass(Wn1, Wn2), Butterworth(N))
digitalfilter(Lowpass(Wn), Butterworth(N))
```

where Wn is the cutoff frequency and N is the filter order. There are separate types for filters in TF and ZPK form and conversions between them.

I make no guarantees regarding the correctness of this code. It's not my area of expertise.