reson

A second-order resonant filter.

Syntax

ares reson asig, xcf, xbw [, iscl] [, iskip]

Initialization

iscl (optional, default=0) -- coded scaling factor for resonators. A value of 1 signifies a peak response factor of 1, i.e. all frequencies other than kcf are attenuated in accordance with the (normalized) response curve. A value of 2 raises the response factor so that its overall RMS value equals 1. (This intended equalization of input and output power assumes all frequencies are physically present; hence it is most applicable to white noise.) A zero value signifies no scaling of the signal, leaving that to some later adjustment (see balance). The default value is 0.

iskip (optional, default=0) -- initial disposition of internal data space. Since filtering incorporates a feedback loop of previous output, the initial status of the storage space used is significant. A zero value will clear the space; a non-zero value will allow previous information to remain. The default value is 0.

Performance

ares -- the output signal at audio rate.

asig -- the input signal at audio rate.

xcf -- the center frequency of the filter, or frequency position of the peak response.

xbw -- bandwidth of the filter (the Hz difference between the upper and lower half-power points).

reson is a second-order filter in which kcf controls the center frequency, or frequency position of the peak response, and kbw controls its bandwidth (the frequency difference between the upper and lower half-power points).

Examples

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

<CsoundSynthesizer>
<CsOptions>
; Select audio/midi flags here according to platform
-odac   ;;;realtime audio out
;-iadc    ;;;uncomment -iadc if realtime audio input is needed too
; For Non-realtime ouput leave only the line below:
; -o reson.wav -W ;;; for file output any platform
</CsOptions>
<CsInstruments>

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

instr 1

asaw vco2 .2, 220       ;sawtooth
kcf  line 220, p3, 1760 ;vary cut-off frequency from 220 to 1280 Hz
kbw  = p4               ;vary bandwidth of filter too           
ares reson asaw, kcf, kbw
asig balance ares, asaw
     outs asig, asig

endin
</CsInstruments>
<CsScore>

i 1 0 4 10      ;bandwidth of filter = 10 Hz
i 1 + 4 50      ;50 Hz and
i 1 + 4 200     ;200 Hz
e
</CsScore>
</CsoundSynthesizer>

A musical example featuring the reson opcode: ResonPluck_Cucchi.csd by Stefano Cucchi.

See also

Standard Filters: Resonant Low-pass filters

Credits

Audio rate parameters introduced in version 6.02

November 2013.