lpf18 lpf18 lpf18 A 3-pole sweepable resonant lowpass filter. Implementation of a 3 pole sweepable resonant lowpass filter. ares lpf18 asig, kfco, kres, kdist 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. This filter requires that the input signal be normalized to one. Here is an example of the lpf18 opcode. It uses the file lpf18.csd. See the sections Real-time Audio and Command Line Flags for more information on using command line flags. Author: Josep M Comajuncosas Spain December 2000 Example written by &namekevin; with help from Iain Duncan. Thanks goes to Iain for helping with the example. New in Csound version 4.10