butterbp
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## butterbp

butterbp — A band-pass Butterworth filter.

## Description

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

## Syntax

    ares butterbp asig, xfreq, xband [, iskip]

## Initialization

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

## Performance

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.

## Examples

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

Example 109. Example of the butterbp opcode.

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

    <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 butterbp.wav -W ;;; for file output any platform
    </CsOptions>
    <CsInstruments>

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

    instr 1	; White noise signal

    asig rand 0.6
         outs asig, asig

    endin

    instr 2	;filtered noise

    asig rand 1
    abp  butterbp asig, 2000, 100	;passing only 1950 to 2050 Hz
         outs abp, abp

    endin

    </CsInstruments>
    <CsScore>

    i 1 0 2
    i 2 2.5 2
    e

    </CsScore>
    </CsoundSynthesizer>

## See Also

butterbr, butterhp, butterlp

## Credits

Author: Paris Smaragdis
MIT, Cambridge
1995

Existed in 3.30

Audio rate parameters introduced in version 6.02

October 2013.

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