Fix firwin() calls with estimate_filter_length()

[MattCarrickPL]

Cataloging firwin() calls that need:

1. a derived transition bandwidth, rather than hard coded (ex: 0.02)
2. Number of taps from estimate_filter_length()
3. a specified fs=1 (firwin assumes fs=2)

from transforms/signal_processing/functional.py:

70 num_taps = int(2np.ceil(502np.pi/new_rate/.125/22)) # fred harris rule of thumb * 2
71 taps = signal.firwin(
72 num_taps,
73 new_rate0.98,
74 width=new_rate * .02,
75 window=signal.get_window("blackman", num_taps),
76 scale=True
77 )

from transforms/signal_processing/sp_functional.py:

70 num_taps = int(2np.ceil(502np.pi/new_rate/.125/22)) # fred harris rule of thumb * 2
71 taps = signal.firwin(
72 num_taps,
73 new_rate0.98,
74 width=new_rate * .02,
75 window=signal.get_window("blackman", num_taps),
76 scale=True
77 )

from transforms/system_impairment/si_functional.py:

115 num_taps = int(2np.ceil(502*np.pi/(1/up)/.125/22)) # fred harris rule of thumb * 2
116 taps = sp.firwin(
117 num_taps,
118 (1/up),
119 width=(1/up) * .02,
120 window=sp.get_window("blackman", num_taps),
121 scale=True
122 )

130 num_taps = int(2 * np.ceil(50 * 2 * np.pi / (1/up) / .125 / 22)) # fred harris rule-of-thumb * 2
131 taps = sp.firwin(
132 num_taps,
133 1 / up,
134 width=(1/up) * .02,
135 window=sp.get_window("blackman", num_taps),
136 scale=True
137 )

354 taps = sp.firwin(
355 num_taps,
356 bandwidth,
357 width=bandwidth * .02,
358 window=sp.get_window("blackman", num_taps),
359 scale=True
360 )

Similar function calls in transforms/system_impairment/functional.py

[gvanhoy]

We don't need a whole filter design suite, but at least a function that gives a reasonably-well designed filter for what we tend to use it for in this library would be great.

[MattCarrickPL]

We can still use firwin() but we need to update the function calls. It uses a filter length approximation that generates filters that are too long and assumes a static transition bandwidth of 1% which is quite narrow and impractical for real world systems.