ar lpf18 asig, kfco, kres, kdist
Implementation of a 3 pole sweepable resonant lowpass filter.
kfco – the filter cutoff frequency in Hz. Should be in the range 0 to sr/2.
kres – the amount of resonance. Self-oscillation occurs when kres is approximately 1. Shoujld usually be in the range 0 to 1, however, values slightly greater than 1 are possible for more sustained oscillation and an "overdrive" effect.
kdist – amount of distortion. kdist = 0 gives a clean output. kdist > 0 adds tanh() distortion controlled by the filter parameters, in such a way that both low cutoff and high resonance increase the distortion amount. Some experimentation is encouraged.
lpf18 is a digital emulation of a 3 pole (18 dB/oct.) lowpass filter capable of self-oscillation with a built-in distortion unit. It is really a 3-pole version of moogvcf, retuned, recalibrated and with some performance improvements. The tuning and feedback tables use no more than 6 adds and 6 multiplies per control rate. The distortion unit, itself, is based on a modified tanh() function driven by the filter controls.
Note: This filter requires that the input signal be normalized to one.
Josep M Comajuncosas
New in Csound Version 4.16