
GAMMATONE  Gammatone filter coefficients
Usage:
 [b,a] = gammatone(fc,fs,n,betamul);
 [b,a] = gammatone(fc,fs,n);
 [b,a] = gammatone(fc,fs);
Input parameters:
 fc  center frequency in Hz.
 fs  sampling rate in Hz.
 n  filter order.
 beta  bandwidth of the filter.
Output parameters:
 b  nominator coefficients.
 a  denominator coefficients.
Description:
GAMMATONE(fc,fs,n,betamul) computes the filter coefficients of a digital
gammatone filter with center frequency fc, order n, sampling rate fs and
bandwith determined by betamul. The bandwidth beta of each filter is
determined as betamul times AUDFILTBW of the center frequency of
corresponding filter.
GAMMATONE(fc,fs,n) will do the same but choose a filter bandwidth
according to Glasberg and Moore (1990). The order n can only be 2 or
4. If the order is 4 then betamul is choosen to be 1.0183 and if the
order is 2 then betamul is choosen to be 0.637.
GAMMATONE(fc,fs) will do as above for a 4th order filter.
If fc is a vector, each entry of fc is considered as one center
frequency, and the corresponding coefficients are returned as row
vectors in the output.
The inpulse response of the gammatone filter is given by
The gammatone filters as implemented by this function generate
complex valued output, because the filters are modulated by the
exponential function. Using REAL on the output will give the
coefficients of the corresponding cosine modulated filters.
To create the filter coefficients of a 1erb spaced filter bank using
gammatone filters use the following construction
[b,a] = gammatone(fs,erbspacebw(flow,fhigh));
References:
A. Aertsen and P. Johannesma.
Spectrotemporal receptive fields of auditory neurons in the
grassfrog. I. Characterization of tonal and natural stimuli.
Biol. Cybern, 38:223234, 1980.
B. Glasberg and B. Moore.
Derivation of auditory filter shapes from notchednoise data.
Hearing Research, 47(12):103, 1990.
