DPW Multi-Waveform Oscillator

Tim Kleinert

Hi folks,

I no longer own a G2, but still use the demo software frequently to quickly try out DSP concepts in order to see if I understood them correctly.

This low-level patch generates sawtooth, triangle and (variable) pulse waves simultaneously from one oscillator core (something lacking in the G2 modules), using extended Differentiated Parabolic Waveform (DPW) techniques. The neat thing about this is that the differentiation and amplitude scaling only has to be done once for the mix of waveforms.

DPW is referred to as an "aliasing-suppressive" technique, as it isn't a true (quasi-)bandlimited method. Nevertheless I think it's quite ingenious in its simplicity, and the results are remarkable given the fact that the naive waveform discontinuities are smoothed by only one transitional sample. At 96kHz it's really not bad at all.

The circuit only uses 9.3% cycles. (The editor shows 11%, but that's the output module.) If memory usage and the slightly off tuning (due to numerical limitations) aren't an issue, it might even be useful. Laughing

I deliberately didn't use a switchable mixer for the waveform mix, because such abrupt amplitude changes cause loud spikes in the following differentiation stage.

There are some neat super-cheap tricks in there like the z-1 differentiator (2 mixers) and a Goldschmidt converger for the fs/f amplitude scaling (1 mixer and amp).

cheers,
t

DPW-MultiWave_TK.pch2

Description:

Simultaneous saw, tri and pulse outputs; aliasing-suppressive DPW method

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DPW-MultiWave_TK.pch2

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