Raspberry Pi Music Synthesis : introduction to wavetables




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Published on Mar 27, 2015

The wavetable synthesis system for the Pi is the newest development, and as a result is the one I have to date explored least. Here's a very quick introduction to what's in place.

In brief -
* a wavetable is a single cycle of a waveform, captured via sampling or computed
* wavetables are antialiased via sort of MIP maps, with a wave per octave
* 2 oscillators per note, the second may be empty and if so is optimized away
* each oscillator is driven by a wavetable trajectory consisting of up 8 wavetables
* OSCB may be up- or down-tuned by a pythagorean fifth relative to A
* the detune table contains many pythagorean intervals, so sounds ultra-sweet when locked in
* each polyphonic synth has 2 LFOs, one dedicated to pitch modulation via Mod Wheel
* both oscillators may be pitch or amplitude modulated by the general-purpose LFO
* a single Envelope Generator is provided for overall level

This was conceived as a half-way house between simple sample replay and full Virtual Analog flexibility, and as such is a much simpler, more CPU-light synth than the Virtual Analog engine, featuring none of the latter's rich arithmetic modulation. But despite its simplicity and efficiency it is still capable of some very cool, rich sounds - it excels at those glacial early 1980s things, and swept wavetables can approximate dynamically filtered, morphed or phase distorted sounds based on the tables used, so not only does it make for great beds and pads as a 4-note polyphony chord engine, it can also replace basses and leads that would otherwise use a Virtual Analog monosynth.

4 notes of wavetable polyphony costs about as much CPU as a single Virtual Analog monosynth, so it's a good trade-off.


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