A command to filter a Sound by a fourth order gammatone bandpass filter.
The impulse response of the filter is a 4-th order gammatone. The filter is implemented as the convolution of the gammatone with the sound. The gain of the filter is scaled to unity at the centre frequency.
The old implementation with a simple 8-th order recursive digital filter with 4 zeros and 8 poles (these 8 poles consist of one conjugate pole pair to the 4-th power) as suggested by Slaney (1993) was not stable for low frequencies.
© djmw, August 29, 2017