The Auditory Modeling Toolbox
DRNL - Dual Resonance Nonlinear Filterbank
Usage
outsig = drnl(insig,fs);
Description
drnl(insig,fs) computes the Dual Resonance Non-Linear (DRNL) filterbank of the input signal insig sampled at fs Hz with channels specified by the center frequencies in fc. The DRNL is described in the paper Lopez-Poveda and Meddis (2001). The DRNL models the basilar membrane non-linearity.
This version of the DRNL incoorperate the middle-ear filter used in Lopez-Poveda and Meddis (2001).
The DRNL takes a lot of parameters which vary over frequency. Such a parameter is described by a \(1 \times 2\) vector [b a] and indicates that the value of the parameter at frequency fc can be calculated by
The parameters are:
| 'flow',flow | Set the lowest frequency in the filterbank to flow. Default value is 80 Hz. |
| 'fhigh',fhigh | Set the highest frequency in the filterbank to fhigh. Default value is 8000 Hz. |
| 'basef',basef | Ensure that the frequency basef is a centre frequency in the filterbank. The default value of [] means no default. |
| 'middleear' | Perform middleear filtering before the actual DRNL is applied using the middleear filter specified in Lopez-Poveda and Meddis (2001), and compensate for the effect of the filter after DRNL filtering. This is the default. |
| 'nomiddleear' | No middle-ear filtering. Be carefull with this setting, as another scaling must then be perform to convert the input to stapes movement. |
| 'bothparts' | Compute both the linear and the non-linear path of the DRNL. This is the default. |
| 'linonly' | Compute only the linear path. |
| 'nlinonly' | Compute only the non-linear path. |
| 'lin_ngt',n | Number of cascaded gammatone filter in the linear part, default value is 2. |
| 'lin_nlp',n | Number of cascaded lowpass filters in the linear part, default value is 4 |
| 'lin_gain',g | Gain in the linear part, default value is [4.20405 ... .47909]. |
| 'lin_fc',fc | Centre frequencies of the gammatone filters in the linear part. Default value is [-0.06762 1.01679]. |
| 'lin_bw',bw | Bandwidth of the gammatone filters in the linear part. Default value is [.03728 .78563] |
| 'lin_lp_cutoff',c | Cutoff frequency of the lowpass filters in the linear part. Default value is [-0.06762 1.01679 ] |
| 'nlin_ngt_before',n | Number of cascaded gammatone filters in the non-linear part before the broken stick non-linearity. Default value is 3. |
| 'nlin_ngt_after',n | Number of cascaded gammatone filters in the non-linear part after the broken stick non-linearity. The default value of [] means to use the 'before' value. |
| 'nlin_nlp',n | Number of cascaded lowpass filters in the non-linear part. Default value is 3. |
| 'nlin_fc_before',fc | Center frequencies of the gammatone filters in the non-linear part before the broken stick non-linearity. Default value is [-0.05252 1.01650]. |
| 'nlin_fc_after',fc | Center frequencies of the gammatone filters in the non-linear part after the broken stick non-linearity. The default value of [] means to use the 'before' value. |
| 'nlin_bw_before',bw | Bandwidth of the gammatone filters in the non-linear part before the broken stick non-linearity. Default value is [-0.03193 .77426 ]. |
| 'nlin_bw_after',w | Bandwidth of the gammatone filters in the non-linear part after the broken stick non-linearity. The default value of [] means to use the 'before' value. |
| 'nlin_lp_cutoff',c | Cutoff frequency of the lowpass filters in the non-linear part. Default value is [-0.05252 1.01650 ]. |
| 'nlin_a',a | The a coefficient for the broken-stick non-linearity. Default value is [1.40298 .81916 ]. |
| 'nlin_b',b | The b coefficient for the broken-stick non-linearity. Default value is [1.61912 -.81867]. |
| 'nlin_c',c | The c coefficient for the broken-stick non-linearity. Default value is [-.60206 0]. |
| 'nlin_d',d | The d coefficient for the broken-stick non-linearity. Default value is 1. |
The output from DRNL can be conveniently visualized using the plotfilterbank function from LTFAT.
References:
E. Lopez-Poveda and R. Meddis. A human nonlinear cochlear filterbank. J. Acoust. Soc. Am., 110:3107-3118, 2001.
R. Meddis, L. O'Mard, and E. Lopez-Poveda. A computational algorithm for computing nonlinear auditory frequency selectivity. J. Acoust. Soc. Am., 109:2852-2861, 2001.
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