fofilter
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## fofilter

fofilter — Formant filter.

## Description

Fofilter generates a stream of overlapping sinewave grains, when fed with a pulse train. Each grain is the impulse response of a combination of two BP filters. The grains are defined by their attack time (determining the skirtwidth of the formant region at -60dB) and decay time (-6dB bandwidth). Overlapping will occur when 1/freq < decay, but, unlike FOF, there is no upper limit on the number of overlaps. The original idea for this opcode came from J McCartney's formlet class in SuperCollider, but this is possibly implemented differently(?).

## Syntax

    asig fofilter ain, kcf, kris, kdec[, istor]

## Initialization

istor --initial disposition of internal data space. Since filtering incorporates a feedback loop of previous output, the initial status of the storage space used is significant. A zero value will clear the space; a non-zero value will allow previous information to remain. The default value is 0.

## Performance

asig -- input signal.

kcf -- filter centre frequency

kris -- impulse response attack time (secs).

kdec -- impulse response decay time (secs).

## Examples

Example 193. Example

    kfe         expseg 10, p3*0.9, 180, p3*0.1, 175
    kenv        linen  1000, 0.05, p3, 0.05
    asig        buzz   kenv, kfe, sr/(2*kfe), 1
    afil        fofilter  asig, 900, 0.007, 0.04

                out afil

## Credits

Author: Victor Lazzarini;
January 2005

New plugin in version 5

January 2005.

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