clfilt

Name

clfilt --  Implements low-pass and high-pass filters of different styles.

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

ar 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. 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 */
        

Credits

Author: Erik Spjut

New in version 4.20