lowpass2 — A resonant lowpass filter.
iskip -- initial disposition of internal data space. A zero value will clear the space; a non-zero value will allow previous information to remain. The default value is 0.
asig -- input signal to be filtered
kcf -- cutoff or resonant frequency of the filter, measured in Hz
kq -- Q of the filter, defined, for bandpass filters, as bandwidth/cutoff. kq should be between 1 and 500
lowpass2 is a second order IIR lowpass filter, with k-rate controls for cutoff frequency (kcf) and Q (kq). As kq is increased, a resonant peak forms around the cutoff frequency, transforming the lowpass filter response into a response that is similar to a bandpass filter, but with more low frequency energy. This corresponds to an increase in the magnitude and "sharpness" of the resonant peak. For high values of kq, a scaling function such as balance may be required. In practice, this allows for the simulation of the voltage-controlled filters of analog synthesizers, or for the creation of a pitch of constant amplitude while filtering white noise.
Here is an example of the lowpass2 opcode. Play lowpass2.csd
Example 540. Example of the lowpass2 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 ; Audio out Audio in -odac ;;;RT audio out ; For Non-realtime ouput leave only the line below: ;-o lpf18.wav -W ;;; for file output any platform </CsOptions> <CsInstruments> ; by Sean Costello sr = 44100 ksmps = 32 nchnls = 2 0dbfs = 1 instr 1 idur = p3 ifreq = p4 iamp = p5 iharms = (sr*.4) / ifreq asig gbuzz .3, ifreq, iharms, 1, .9, 1 ; Sawtooth-like waveform kfreq linseg 1, idur * 0.5, 5000, idur * 0.5, 1 ; Envelope to control filter cutoff afilt lowpass2 asig,kfreq, 30 kenv linseg 0, .1, iamp, idur -.2, iamp, .1, 0 ; Simple amplitude envelope outs afilt * kenv, afilt * kenv endin </CsInstruments> <CsScore> f1 0 8192 9 1 1 .25 ; frq amp i1 0 5 100 .15 i1 5 5 200 .12 e </CsScore> </CsoundSynthesizer>