[SciPy-Dev] Proposed API change for some functions in scipy.signal

[Warren Weckesser]

I've been using quite a few of the functions in scipy.signal recently, and
I've been reminded of some of the quirks of the API. I have submitted a
pull request to clean up one of those quirks.

In the new pull request, I have added the argument 'fs' (the sampling
frequency) to the following functions:  firwin, firwin2, firls, and remez.
For firwin, firwin2 and firls, the new argument replaces 'nyq', and for
remez, it replaces 'Hz'.  This makes these functions consistent with the
other functions in which the sampling frequency is specified using 'fs':
periodogram, welch, csd, coherence, spectrogram, stft, and istft. 'fs', or
in LaTeX, $f_s$, is common notation for the sampling frequency in the DSP
literature.

In the pull request, the old argument is given a "soft" deprecation. That
means the docstring says the argument is deprecated, but code to actually
generate a DeprecationWarning has not been added yet.  I'm fine with adding
that now, but some might prefer a relatively long and soft transition for
these changes.  (Personally, I don't mind if they hang around for a while,
but they should be gone by 2.0. :)

I haven't changed the default value of the sampling frequency.  For the FIR
filter design functions firls, firwin and firwin2, the default is nyq=1.0
(equivalent to fs=2), while for remez the default is Hz=1 (i.e. fs=1).  The
functions that currently already use 'fs' all have the default fs=1.
Changing the default for the FIR design functions would be a much more
disruptive change.

Comments here or on the pull request are welcome.

P.S. I can see future pull requests in which 'fs' is added to functions
that currently don't have an argument to specify the sampling frequency.
I'm looking at you, freqz.
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