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. It uses the file 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>