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.
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.
asig -- The input audio signal.
kfreq -- The corner frequency for low-pass or high-pass.
Here is an example of the clfilt opcode as a low-pass filter. It uses the files clfilt_lowpass.orc and clfilt_lowpass.sco.
Example 15-1. Example of the clfilt opcode as a low-pass filter.
/* clfilt_lowpass.orc */
; Initialize the global variables.
sr = 22050
kr = 2205
ksmps = 10
nchnls = 1
; Instrument #1 - an unfiltered noise waveform.
instr 1
; White noise signal
asig rand 22050
out asig
endin
; Instrument #2 - a filtered noise waveform.
instr 2
; White noise signal
asig rand 22050
; Lowpass filter signal asig with a
; 10-pole Butterworth at 500 Hz.
a1 clfilt asig, 500, 0, 10
out a1
endin
/* clfilt_lowpass.orc */
/* clfilt_lowpass.sco */
; Play Instrument #1 for two seconds.
i 1 0 2
; Play Instrument #2 for two seconds.
i 2 2 2
e
/* clfilt_lowpass.sco */
Here is an example of the clfilt opcode as a high-pass filter. It uses the files clfilt_highpass.orc and clfilt_highpass.sco.
Example 15-2. Example of the clfilt opcode as a high-pass filter.
/* clfilt_highpass.orc */
; Initialize the global variables.
sr = 22050
kr = 2205
ksmps = 10
nchnls = 1
; Instrument #1 - an unfiltered noise waveform.
instr 1
; White noise signal
asig rand 22050
out asig
endin
; Instrument #2 - a filtered noise waveform.
instr 2
; White noise signal
asig rand 22050
; 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
out a1
endin
/* clfilt_highpass.orc */
/* clfilt_highpass.sco */
; Play Instrument #1 for two seconds.
i 1 0 2
; Play Instrument #2 for two seconds.
i 2 2 2
e
/* clfilt_highpass.sco */