moogladder

Moog ladder lowpass filter.

Moogladder is an new digital implementation of the Moog ladder filter based on the work of Antti Huovilainen, described in the paper "Non-Linear Digital Implementation of the Moog Ladder Filter" (Proceedings of DaFX04, Univ of Napoli). This implementation is probably a more accurate digital representation of the original analogue filter.

Syntax

asig moogladder ain, kcf, kres[, istor]
asig moogladder ain, acf, kres[, istor]
asig moogladder ain, kcf, ares[, istor]
asig moogladder ain, acf, ares[, istor]

Initialization

istor --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

asig -- input signal.

kcf/acf -- filter cutoff frequency

kres/ares -- resonance, generally < 1, but not limited to it. Higher than 1 resonance values might cause aliasing, analogue synths generally allow resonances to be above 1.

Examples

Here is an example of the moogladder opcode. It uses the file moogladder.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 moogladder.wav -W ;;; for file output any platform
</CsOptions>
<CsInstruments>

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

instr 1

kfe  expseg 500, p3*0.9, 1800, p3*0.1, 3000
asig buzz  1, 100, 20, 1
kres line .1, p3, .99   ;increase resonance
afil moogladder asig, kfe, kres
     outs afil, afil

endin
</CsInstruments>
<CsScore>
f 1 0 4096 10 1

i 1 0 10
e
</CsScore>
</CsoundSynthesizer>

See also

Standard Filters: Resonant Low-pass filters

Credits

Author: Victor Lazzarini
January 2005

New plugin in version 5

January 2005.

Audio rate parameters introduced in version 6.02

October 2013.