fofilter

Formant filter.

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, xcf, xris, xdec[, 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.

xcf -- filter centre frequency

xris -- impulse response attack time (secs).

xdec -- impulse response decay time (secs).

Examples

Here is an example of the fofilter opcode. It uses the file fofilter.csd.

<CsoundSynthesizer>
<CsOptions>
; Select audio/midi flags here according to platform
-odac     ;;;realtime audio out
;-iadc    ;;;uncomment -iadc if realtime audio input is needed too
; For Non-realtime ouput leave only the line below:
; -o fofilter.wav -W ;;; for file output any platform
</CsOptions>
<CsInstruments>

sr = 44100
ksmps = 32  
nchnls = 2
0dbfs  = 1

instr 1

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

endin
</CsInstruments>
<CsScore>
; sine wave
f 1 0 16384 10 1

i 1 0 10
e
</CsScore>
</CsoundSynthesizer>

See also

Specialized Filters: Other filters

Credits

Author: Victor Lazzarini
January 2005

New plugin in version 5

Audio rate parameters introduced in version 6.02

November 2013.