ar lowpass2 asig, kcf, kq[, iskip]
Implementation of resonant second-order 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.
; Orchestra file for resonant filter sweep of a sawtooth-like waveform. sr = 44100 kr = 2205 ksmps = 20 nchnls = 1 instr 1 idur = p3 ifreq = p4 iamp = p5 * .5 iharms = (sr*.4) / ifreq ; Sawtooth-like waveform asig gbuzz 1, ifreq, iharms, 1, .9, 1 ; Envelope to control filter cutoff kfreq linseg 1, idur * 0.5, 5000, idur * 0.5, 1 afilt lowpass2 asig, kfreq, 30 ; Simple amplitude envelope kenv linseg 0, .1, iamp, idur -.2, iamp, .1, 0 out asig * kenv endin ; Score file for above f1 0 8192 9 1 1 .25 i1 0 5 100 1000 i1 5 5 200 1000 e
Seattle, Washington August, 1999
New in Csound version 4.0