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Centre Frequency modes

There are several centre frequency modes available, and the mode chosen defines how many parameters must be given in the parameter file. For the "BasilarM_GammaT" module the centre frequency mode is specified on line two of the parameter file, as shown in figure [27]. In the case of parameter file (A) in figure [27] where the "SINGLE" mode is used, only one parameter is required, i.e. the filter centre frequency (CF). In parameter file (B) the "LOG" centre frequency mode is used, while will produce a filter-bank with a range of centre frequencies equally spaced on a logarithmic scale. It requires three parameters i.e. the initial and final centre frequencies and the number of filter channels required for the filter-bank.

The centre frequency mode can be specified in upper or lower case, thus "Single", "single" and "SINGLE" are equivalent. The order of the parameters after the mode specification is important, i.e. , for parameter file (B) in figure [27] the first value will be taken as the initial centre frequency of the filter bank, the second as the final centre frequency, and the third as the number of filter-bank channels required. If the correct number of parameters is not provided in a parameter file, then an error will occur in reading the parameters from the file. As with all parameter files, only the first field or value is significant. The remaining text on a line is ignored, and can be used to supply descriptive comments. White space must separate the field value and any additional text.

The available frequency modes are given below in table [2]. The centre frequencies are controlled by the UtCFList utilities module.

Mode

Description
Required Parameters
ERB
Filter-bank with centre frequencies equally spaced on an equivalent rectangular bandwidth (ERB) scale (Glasberg & Moore, 1990).
(1) Initial filter-bank CF (Hz).

(2) Final filter-bank CF (Hz).

(3) ERB rate (Hz).

LINEAR
Filter-bank with centre frequencies equally spaced on a linear scale.
(1) Initial filter-bank CF (Hz).

(2) Final filter-bank CF (Hz).

(3) Number of filter-bank output channels (integer).

LOG
Filter-bank with centre frequencies equally spaced on a logarithmic scale.
(1) Initial filter-bank CF (Hz).

(2) Final filter-bank CF (Hz).

(3) Number of filter-bank output channels (integer).

SINGLE
Single filter mode
(1) Filter CF (Hz).
USER
Filter-bank with a custom centre frequency list, as specified by the user.
(1) Number of filter-bank output channels (integer).

(..) CF list - one line for each CF (Hz). The number of lines must correspond with the number of filter-bank output channels specified.

Table [2]: The centre frequency (CF) modes available for the basilar membrane filter modules.

The routines in the UtCFList utilities module can also be used to produce frequency lists which can be used for purposes other than creating a filter-bank. For example, the routines are used for specifying the frequencies at which the output characteristics of a single filter are investigated in the Tests/ Combinations/FilterShape.c test program.


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