[SciPy-Dev] Nyquist Filters

[Warren Weckesser]

On Mon, Aug 25, 2014 at 6:55 PM, Jeff Grasty <jeff.grasty at gmail.com> wrote:

> Hi,
>
> One of the features that I have found missing in SciPy are functions to
> design nyquist and root-nyquist filters, such as raised cosine and
> root-raised cosine filters.  I have written several functions for this
> purpose and was curious if anyone thought was a greater need for this.
>
>

Yes, that would be great!  I have some scratch work for the raised cosine
and root-raised cosine FIR filters, but they're not ready for contributing
to scipy.  If you have code in pretty good shape, these would be nice
additions to scipy.signal.

The first thing to think about is the API.  What is the API of your code?

A possible design is similar to the Savitzy-Golay filter implementation.
It's a very basic, function-oriented API.  One function, savgol_coeffs,
provides the FIR filter coefficients, given the number of taps and the
parameters of the filter.  Another function, savgol_filter, takes an input
array along with the filter parameters.  It computes the coefficients and
applies the filter.  It is really just a convenience function: it calls
savgol_coeffs to compute the filter coefficients, and applies the filter
using a convolution (the only complication is that it provides several
options for handling the edges of the input).  Even more basic are the
functions for FIR filter design using the window method.  The functions
firwin and firwin2 compute the filter coefficients, and leave it up to the
user to convolve them with their signal.

Looking forward to hearing more.

Warren



Thanks,
> Jeff
>
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