Name
Treble -- tone control: RBJ shelving biquad IIR filter
Synopsis
treble gain [frequency[k] [width[s|h|k|o|q]]]
Function
Boost or cut the treble (upper) frequencies of the audio using a two-pole shelving filter with a response similar to that of a standard hi-fi's tone-controls. This is also known as shelving equalisation (EQ).

gain gives the gain at whichever is the lower of -22 kHz and the Nyquist frequency. Its useful range is about -20 (for a large cut) to +20 (for a large boost). Beware of clipping when using a positive gain.

If desired, the filter can be fine-tuned using the following optional parameters:

frequency sets the filter's central frequency and so can be used to extend or reduce the frequency range to be boosted or cut. The default value is 3 kHz.

width determines how steep is the filter's shelf transition. In addition to the common width specification methods described above, "slope" (the default, or if appended with "s") may be used. The useful range of "slope" is about 0.3, for a gentle slope, to 1 (the maximum), for a steep slope; the default value is 0.5.

See also equalizer for a peaking equalisation effect.

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