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Signal Modifiers: Standard Filters

lpf18

  ar      lpf18      asig, kfco, kres, kdist

Description

Implementation of a 3 pole sweepable resonant lowpass filter.

Performance

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.

Author

Josep M Comajuncosas
Spain
December, 2000
New in Csound Version 4.16


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Signal Modifiers: Standard Filters