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[py] improve style for demo_filterbank.py

--- a/python/demos/demo_filterbank.py

+++ b/python/demos/demo_filterbank.py

@@ -1,30 +1,44 @@

 #! /usr/bin/env python

-from aubio import filterbank, fvec

-from pylab import loglog, show, xlim, ylim, xlabel, ylabel, title

-from numpy import vstack, arange

+"""Create a filterbank from a list of frequencies.

-win_s = 2048

+This demo uses `aubio.filterbank.set_triangle_bands` to build a set of

+triangular filters from a list of frequencies.

+

+The filterbank coefficients are then modified before being displayed."""

+

+import aubio

+import numpy as np

+import matplotlib.pyplot as plt

+

+# sampling rate and size of the fft

 samplerate = 48000

+win_s = 2048

+# define a list of custom frequency

 freq_list = [60, 80, 200, 400, 800, 1600, 3200, 6400, 12800, 24000]

+# number of filters to create

 n_filters = len(freq_list) - 2

-f = filterbank(n_filters, win_s)

-freqs = fvec(freq_list)

+# create a new filterbank

+f = aubio.filterbank(n_filters, win_s)

+freqs = aubio.fvec(freq_list)

 f.set_triangle_bands(freqs, samplerate)

+# get the coefficients from the filterbank

 coeffs = f.get_coeffs()

-coeffs[4] *= 5.

-

+# apply a gain to fifth band

+coeffs[4] *= 6.

+# load the modified coeffs into the filterbank

 f.set_coeffs(coeffs)

-times = vstack([arange(win_s // 2 + 1) * samplerate / win_s] * n_filters)

-title('Bank of filters built using a simple list of boundaries\nThe middle band has been amplified by 2.')

-loglog(times.T, f.get_coeffs().T, '.-')

-xlim([50, samplerate/2])

-ylim([1.0e-6, 2.0e-2])

-xlabel('log frequency (Hz)')

-ylabel('log amplitude')

-

-show()

+# display the band gains in a loglog plot

+freqs = np.vstack([np.arange(win_s // 2 + 1) * samplerate / win_s] * n_filters)

+plt.title('filterbank built from a list of frequencies\n'

+          'The 5th band has been amplified by a factor 6.')

+plt.loglog(freqs.T, f.get_coeffs().T, '.-')

+plt.xlim([50, samplerate/2])

+plt.ylim([1.0e-6, 2.0e-2])

+plt.xlabel('log frequency (Hz)')

+plt.ylabel('log amplitude')

+plt.show()