Raspberry Pi Music Synthesis : Virtual Analog oscillator walkthrough & introduction to wavetables

Published on Mar 27, 2015 Pi Synth

"A very quick run through of what the oscillators can do under my Raspberry Pi Virtual Analog synthesis model. Each monosynth has a pair of full-feature oscillators OSCA and OSCB, plus a sub-oscillator OSCC which may be configured as a sinusoidal sub-bass oscillator or as a noise generator. Each full-fat oscillator supports limited Phase Distortion (effectively PWM of any shape wave), smooth morphing of the wave between a pair of endpoints (e.g. sin to square, or saw to sin), and the oscillators' pitch, Phase Distortion, level and morph may be driven by a outputs from the modulation matrix. Modulation outputs are an arithmetic combination of an EG, an LFO, a constant offset, and a continuous controller. The envelope generators take 'Velocity' as a programming parameter to support piano-like vs. organ-like playing, and additionally the Envelope Generators support a 'sustain half-life' parameter, so rather than ADSR they are ADSλRV.

Note that I largely play 'F' throughout. This makes for dull listening but more educational viewing - the global tuning for the synth has been tweaked slightly away from concert pitch. F1 - normally 43.654Hz - is retuned to 43.0664Hz, which is 44100 / 1024, ensuring the waveform remains stationary on screen, at least in the absence of frequency modulation or pitch bends. Also note that this demo only shows one rather than two waveforms on screen - the software auto-detects a mono signal, and pulls back to one wave. As soon as stereo is detected the second waveforms jumps back."

Raspberry Pi Music Synthesis : introduction to wavetables

Published on Mar 27, 2015

"The wavetable synthesis system for the Pi is the newest and 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
* 2 oscillators per note
* each oscillator driven by a wavetable trajectory through up to 8 wavetables
* 2 LFOs, one dedicated to pitch modulation via Mod Wheel
* single Envelope Generator for overall level

This is deisgned to be a much simpler, more CPU-light synth than the Virtual Analog engine, and so has none of the rich arithmetic modulation, but is still capable of some very cool sounds, and excels at those glacial early 1980s things - it makes for great beds and pads as a 4-note polyphony chord engine, and 4 notes of wavetable polyphony costs about as much CPU as a single Virtual Analog monosynth, so it's a good trade-off."