butterbr — A band-reject Butterworth filter.


Implementation of a second-order band-reject Butterworth filter. This opcode can also be written as butbr.


ares butterbr asig, xfreq, xband [, 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.

xfreq -- Cutoff or center frequency for each of the filters.

xband -- Bandwidth of the bandpass and bandreject filters.


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

Example 112. Example of the butterbr 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 butterbr.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 0.7
abr  butterbr asig, 3000, 2000	;center frequency = 3000, bandwidth =  +/- (2000)/2, so 2000-4000 
     outs abr, abr



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.