HOHMANN2002
Invertible Gammatone filterbank

Usage:

fb = hohman2002(fs, flow, basef, fhigh, filters_per_ERBaud)

Input parameters:

`fs`	The sampling frequency of the signals on which the filterbank will operate
`flow`	The lowest center frequency of a filter
`basef`	"base frequency". One of the filters will have exactly this center frequency. Must be `>= flow`
`fhigh`	The highest center frequency of a filter. Must be `>= basef`
`filters_per_ERBaud`
	The density of gammatone filters on the ERB scale.

Output parameters:

`fb`	The constructed filterbank object.

Description:

hohman2002 constructs a new fb object implementing the analysis part of a gammatone filterbank as described in Hohmann (2002).

fb contains several all-pole gammatone filters; each one with a bandwidth of 1 ERB (optional: times bandwidth_factor), and an order of gamma_order.

The center frequencies of the individual filters are computed as described in section 3 of Hohmann (2002).

hohmann2002 takes the following flags at the end of the line of input arguments:

`'gamma_order'`	The order of the gammatone filters in this filterbank. Default is `4`.
`'bandwidth_factor'`	The bandwidth parameter of the individual filters is calculated from the Equivalent Rectangular Bandwidth (ERB) according to equation 14 in Hohmann (2002). ERB is taken from the Glasberg & Moore formula for a specific center frequency (equation 13 in Hohmann (2002)). Using this parameter, it is possible to widen or narrow all filters of the filterbank with a constant bandwidth factor. Default is `1.0`.
`'l'`	Scaling factor `l` from Eq. 13 in Hohmann (2002). Default is `24.7`.
`'q'`	Scaling factor `q` from Eq. 13 in Hohmann (2002). Default is 9.265.

References:

V. Hohmann. Frequency analysis and synthesis using a gammatone filterbank. Acta Acustica united with Acoustica, 88(3):433--442, 2002.