Description

Implements the classical standard analog filter types: low-pass and high-pass. They are implemented with the four classical kinds of filters: Butterworth, Chebyshev Type I, Chebyshev Type II, and Elliptical. The number of poles may be any even number from 2 to 80.

Syntax

ares clfilt asig, kfreq, itype, inpol [, ikind] [, ipbr] [, isba] [, iskip]

Initialization

itype -- 0 for low-pass, 1 for high-pass.

inpol -- The number of poles in the filter. It must be an even number from 2 to 80.

ikind (optional) -- 0 for Butterworth, 1 for Chebyshev Type I, 2 for Chebyshev Type II, 3 for Elliptical. Defaults to 0 (Butterworth)

ipbr (optional) -- The pass-band ripple in dB. Must be greater than 0. It is ignored by Butterworth and Chebyshev Type II. The default is 1 dB.

isba (optional) -- The stop-band attenuation in dB. Must be less than 0. It is ignored by Butterworth and Chebyshev Type I. The default is -60 dB.

iskip (optional) -- 0 initializes all filter internal states to 0. 1 skips initialization. The default is 0.

Performance

asig -- The input audio signal.

kfreq -- The corner frequency for low-pass or high-pass.

Examples

Here is an example of the clfilt opcode as a low-pass filter. Play clfilt_lowpass.csd

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

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

instr 1	; white noise

asig rand 0.5
outs asig, asig

endin

instr 2	; filtered noise 

asig rand 0.9
; Lowpass filter signal asig with a 
; 10-pole Butterworth at 500 Hz.
a1 clfilt asig, 500, 0, 10
   outs a1, a1

endin

</CsInstruments>
<CsScore>

i 1 0 2
i 2 2 2
e

</CsScore>
</CsoundSynthesizer>

Here is an example of the clfilt opcode as a high-pass filter. Play clfilt_highpass.csd

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

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

instr 1	; white noise

asig rand 0.6
     outs asig, asig

endin

instr 2	;filtered noise

asig rand 0.7
; Highpass filter signal asig with a 6-pole Chebyshev
; Type I at 20 Hz with 3 dB of passband ripple.
a1 clfilt asig, 20, 1, 6, 1, 3
   outs a1, a1

endin

</CsInstruments>
<CsScore>

i 1 0 2
i 2 2 2
e

</CsScore>
</CsoundSynthesizer>

Credits

Author: Erik Spjut

New in version 4.20