[SciPy-Dev] Nyquist Filters

[Neal Becker]

Interesting, but I am maybe missing something.  This optimization only enforces 
flatness in passband and stopband, and 3dB pt.

But nyquist filter is defined as having nyquist symmetry, which is what leads to 
zero ISI (the main reason for using a nyquist filter).  There doesn't appear to 
be anything enforcing this symmmetry.

Jeff Grasty wrote:

> Warren,
> 
> I currently have two functions, Nyquist and rootNyquist, that return the
> coefficients of a nyquist or root-nyquist filter with a specified alpha
> and length.  The algorithm that the functions implement is one proposed
> by Fred Harris in hist multi-rate signal processing book.  It uses the
> remez algorithm to start as an initial guess and uses a gradient
> descent method to adjust the cutoff frequency of the passband until
> the filter's 3 dB (or 6 dB) point is at half the baud rate.
> 
> I think the API that you mentioned for the Savitzky-Golay filter uses
> sounds simple and effective.
> 
> What are ideas of how to test this?  I can think of writing some simple
> unit tests that check filter length, gain, etc.  Would that be sufficient.
> 
> Here is a link to my github project for the code so far:
> https://github.com/fstop22/nyquist_filters
> 
> Thanks,
> Jeff
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