Kurzweil:Four-pole Lowpass with separation

From Sonikmatter

The Four-pole Lowpass with separation filter(4POLE LOPASS W/SEP) is the largest and most complex lowpass filter available on the K2xxx. It uses up 3 DSP blocks, and for single layer sounds is the only processing block that can be used on that layer.

This filter is a combination of the Two-pole Lowpass filter and the Two-pole Lowpass, -6 dB resonance filter, with the filters operating in a serial configuration. The cutoff frequency of both of these sub-filters is controlled with the cutoff frequency control. Resonance is controlled only for the Two-pole Lowpass filter, and the third control is the separation.

The separation allows the cutoff frequency of the Two-pole Lowpass -6dB to be offset from the Two-pole Lowpass filter. This is a very understated control, because it is this control that allows the shape of the filter's rolloff to be controlled.

With the separation set to 0 Hz, the filter has a rolloff of 24 dB/Octave, but by nudging the separation up slightly, the rolloff can be changed to resemble other filters such as the 3 Pole, 18 dB/Octave rolloff of the TB303 filter, and manipulating this parameter in real time essentially allows you to morph the filter characteristics. This is a subtle change, but it can add movement to the sound, and is very useful for evolving pads, where you want something unique.

This filter really comes into it's own when it's used as part of a triple mode program where other DSP Blocks are available for processing.

The Puppeteer 21:34, 6 Jul 2005 (EDT)

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