.. currentmodule:: brian

.. index::
   pair: example usage; erbspace
   pair: example usage; Gammatone
   pair: example usage; whitenoise

.. _example-hears_gammatone:

Example: gammatone (hears)
==========================

Example of the use of the class :class:`~brian.hears.Gammatone` available in the
library. It implements a fitlerbank of IIR gammatone filters as 
described  in Slaney, M., 1993, "An Efficient Implementation of the
Patterson-Holdsworth Auditory Filter Bank". Apple Computer Technical Report #35. 
In this example, a white noise is filtered by a gammatone filterbank and the
resulting cochleogram is plotted.

::

    from brian import *
    from brian.hears import *
    from matplotlib import pyplot
    
    sound = whitenoise(100*ms).ramp()
    sound.level = 50*dB
    
    nbr_center_frequencies = 50
    b1 = 1.019  #factor determining the time constant of the filters
    #center frequencies with a spacing following an ERB scale
    center_frequencies = erbspace(100*Hz, 1000*Hz, nbr_center_frequencies)
    gammatone = Gammatone(sound, center_frequencies, b=b1)
    
    gt_mon = gammatone.process()
    
    figure()
    imshow(gt_mon.T, aspect='auto', origin='lower left',
           extent=(0, sound.duration/ms,
                   center_frequencies[0], center_frequencies[-1]))
    pyplot.yscale('log')
    title('Cochleogram')
    ylabel('Frequency (Hz)')
    xlabel('Time (ms)')
    
    show()