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#!/usr/bin/env python
# plot the waveform and a sonogram for an audio input (e.g. a bird song).
from pylab import *
from matplotlib import *
import wave
import sys
# modified specgram()
# http://stackoverflow.com/questions/19468923/cutting-of-unused-frequencies-in-specgram-matplotlib
def my_specgram(x, NFFT=256, Fs=2, Fc=0, detrend=mlab.detrend_none,
window=mlab.window_hanning, noverlap=128,
cmap=None, xextent=None, pad_to=None, sides='default',
scale_by_freq=None, minfreq = None, maxfreq = None, **kwargs):
"""
call signature::
specgram(x, NFFT=256, Fs=2, Fc=0, detrend=mlab.detrend_none,
window=mlab.window_hanning, noverlap=128,
cmap=None, xextent=None, pad_to=None, sides='default',
scale_by_freq=None, minfreq = None, maxfreq = None, **kwargs)
Compute a spectrogram of data in *x*. Data are split into
*NFFT* length segments and the PSD of each section is
computed. The windowing function *window* is applied to each
segment, and the amount of overlap of each segment is
specified with *noverlap*.
%(PSD)s
*Fc*: integer
The center frequency of *x* (defaults to 0), which offsets
the y extents of the plot to reflect the frequency range used
when a signal is acquired and then filtered and downsampled to
baseband.
*cmap*:
A :class:`matplotlib.cm.Colormap` instance; if *None* use
default determined by rc
*xextent*:
The image extent along the x-axis. xextent = (xmin,xmax)
The default is (0,max(bins)), where bins is the return
value from :func:`mlab.specgram`
*minfreq, maxfreq*
Limits y-axis. Both required
*kwargs*:
Additional kwargs are passed on to imshow which makes the
specgram image
Return value is (*Pxx*, *freqs*, *bins*, *im*):
- *bins* are the time points the spectrogram is calculated over
- *freqs* is an array of frequencies
- *Pxx* is a len(times) x len(freqs) array of power
- *im* is a :class:`matplotlib.image.AxesImage` instance
Note: If *x* is real (i.e. non-complex), only the positive
spectrum is shown. If *x* is complex, both positive and
negative parts of the spectrum are shown. This can be
overridden using the *sides* keyword argument.
**Example:**
.. plot:: mpl_examples/pylab_examples/specgram_demo.py
"""
#####################################
# modified axes.specgram() to limit
# the frequencies plotted
#####################################
# this will fail if there isn't a current axis in the global scope
ax = gca()
Pxx, freqs, bins = mlab.specgram(x, NFFT, Fs, detrend,
window, noverlap, pad_to, sides, scale_by_freq)
# modified here
#####################################
if minfreq is not None and maxfreq is not None:
Pxx = Pxx[(freqs >= minfreq) & (freqs <= maxfreq)]
freqs = freqs[(freqs >= minfreq) & (freqs <= maxfreq)]
#####################################
Z = 10. * np.log10(Pxx)
Z = np.flipud(Z)
if xextent is None: xextent = 0, np.amax(bins)
xmin, xmax = xextent
freqs += Fc
extent = xmin, xmax, freqs[0], freqs[-1]
im = ax.imshow(Z, cmap, extent=extent, **kwargs)
ax.axis('auto')
return Pxx, freqs, bins, im
def sonogram(wav_file, startsecs=None, endsecs=None):
'''Plot a sonogram for the given file,
optionally specifying the start and end time in seconds.
'''
wav = wave.open(wav_file, 'r')
frames = wav.readframes(-1)
frame_rate = wav.getframerate()
chans = wav.getnchannels()
secs = wav.getnframes() / float(frame_rate)
sound_info = pylab.fromstring(frames, 'Int16')
wav.close()
# The wave module doesn't have any way to read just part of a wave file
# (sigh), so we have to take an array slice after we've already read
# the whole thing into numpy.
if startsecs or endsecs:
if not startsecs:
startsecs = 0.0
if not endsecs:
endsecs = secs - startsecs
startpos = startsecs * frame_rate * chans
endpos = endsecs * frame_rate * chans
sound_info = sound_info[startpos:endpos]
secs = endsecs - startsecs
else:
startsecs = 0.0
print secs, "seconds"
t = arange(startsecs, startsecs + secs, 1.0 / frame_rate / chans)
ax1 = subplot(211)
title(wav_file)
plot(t, sound_info)
subplot(212, sharex=ax1)
Pxx, freqs, bins, im = my_specgram(sound_info, Fs=frame_rate*chans,
# cmap=cm.Accent,
minfreq = 0, maxfreq = 10000)
show()
close()
if __name__ == '__main__':
filename = sys.argv[1]
start = None
end = None
if len(sys.argv) > 2:
start = float(sys.argv[2])
print "Starting at", start
if len(sys.argv) > 3:
end = float(sys.argv[3])
print "ending at", end
sonogram(filename, start, end)
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