butterhp — A high-pass Butterworth filter.


Implementation of second-order high-pass Butterworth filter. This opcode can also be written as buthp.


ares butterhp asig, kfreq [, iskip]
ares butterhp asig, afreq [, iskip]


iskip (optional, default=0) -- Skip initialization if present and non-zero.


These filters are Butterworth second-order IIR filters. They are slightly slower than the original filters in Csound, but they offer an almost flat passband and very good precision and stopband attenuation.

asig -- Input signal to be filtered.

kfreq/afreq -- Cutoff or center frequency for each of the filters.


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

Example 113. Example of the butterhp opcode.

See the sections Real-time Audio and Command Line Flags for more information on using command line flags.

; 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 butterhp.wav -W ;;; for file output any platform

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

instr 1	  ; White noise 

asig rand 0.5
outs asig, asig


instr 2	; filtered noise

asig rand 0.6
ahp  butterhp asig, 500  ;pass frequencies above 500 Hz
     outs ahp, ahp



i 1 0 2
i 2 2.5 2


See also

Standard filters: Butterworth filters


Author: Paris Smaragdis
MIT, Cambridge

Existed in 3.30

Audio rate parameters introduced in version 6.02

October 2013.