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Module « scipy.signal »

Fonction gammatone - module scipy.signal

Signature de la fonction gammatone

def gammatone(freq, ftype, order=None, numtaps=None, fs=None) 

Description

help(scipy.signal.gammatone)

Gammatone filter design.

This function computes the coefficients of an FIR or IIR gammatone
digital filter [1]_.

Parameters
----------
freq : float
    Center frequency of the filter (expressed in the same units
    as `fs`).
ftype : {'fir', 'iir'}
    The type of filter the function generates. If 'fir', the function
    will generate an Nth order FIR gammatone filter. If 'iir', the
    function will generate an 8th order digital IIR filter, modeled as
    as 4th order gammatone filter.
order : int, optional
    The order of the filter. Only used when ``ftype='fir'``.
    Default is 4 to model the human auditory system. Must be between
    0 and 24.
numtaps : int, optional
    Length of the filter. Only used when ``ftype='fir'``.
    Default is ``fs*0.015`` if `fs` is greater than 1000,
    15 if `fs` is less than or equal to 1000.
fs : float, optional
    The sampling frequency of the signal. `freq` must be between
    0 and ``fs/2``. Default is 2.

Returns
-------
b, a : ndarray, ndarray
    Numerator (``b``) and denominator (``a``) polynomials of the filter.

Raises
------
ValueError
    If `freq` is less than or equal to 0 or greater than or equal to
    ``fs/2``, if `ftype` is not 'fir' or 'iir', if `order` is less than
    or equal to 0 or greater than 24 when ``ftype='fir'``

See Also
--------
firwin
iirfilter

References
----------
.. [1] Slaney, Malcolm, "An Efficient Implementation of the
    Patterson-Holdsworth Auditory Filter Bank", Apple Computer
    Technical Report 35, 1993, pp.3-8, 34-39.

Examples
--------
16-sample 4th order FIR Gammatone filter centered at 440 Hz

>>> from scipy import signal
>>> signal.gammatone(440, 'fir', numtaps=16, fs=16000)
(array([ 0.00000000e+00,  2.22196719e-07,  1.64942101e-06,  4.99298227e-06,
    1.01993969e-05,  1.63125770e-05,  2.14648940e-05,  2.29947263e-05,
    1.76776931e-05,  2.04980537e-06, -2.72062858e-05, -7.28455299e-05,
   -1.36651076e-04, -2.19066855e-04, -3.18905076e-04, -4.33156712e-04]),
   [1.0])

IIR Gammatone filter centered at 440 Hz

>>> import matplotlib.pyplot as plt
>>> import numpy as np

>>> fc, fs = 440, 16000
>>> b, a = signal.gammatone(fc, 'iir', fs=fs)
>>> w, h = signal.freqz(b, a)
>>> plt.plot(w * fs / (2 * np.pi), 20 * np.log10(abs(h)))
>>> plt.xscale('log')
>>> plt.title('Gammatone filter frequency response')
>>> plt.xlabel('Frequency [Hz]')
>>> plt.ylabel('Amplitude [dB]')
>>> plt.margins(0, 0.1)
>>> plt.grid(which='both', axis='both')
>>> plt.axvline(fc, color='green') # cutoff frequency
>>> plt.show()

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