Phase Distortion Synthesis

What is PD Synthesis?

Phase distortion synthesis (also known as PD) is a form of synthesis initially developed by the Casio company. They presented it for the first time in their CZ series of synthesizers. In the 1980s, Casio`s engineer, Mark Fukuda, invented this form of audio synthesis, which evolved from the Cosmo Synth System. Pursuing this further, Cosmo Synth System was custom-developed for Japanese synthesist-composer Isao Tomita, who is regarded as one of the pioneers of electronic music. Casio used digital synthesis without a filter to make CZ synthesizers less expensive than analog-based subtractive synthesis with a filter.  

Phase Distortion Application

The sound from it was “ thinner “compared to the more expensive analog synthesizers. The phase distortion technique was initially used to simulate analog filters. It had, in total, eight different waveforms. As well as the standard saw-tooth, square, and pulse waveforms had a particular double-sine waveform, a half-sine waveform, and three waveforms with simulated filter resonance: resonant saw-tooth, triangle, and trapezoidal waveforms. Each digital oscillator could have one or two waveforms. Unlike other synthesizers, where having multiple waveforms causes those multiple waveforms to mix (parallel), the CZ synthesizers play one waveform and then play the other, and so on in alternation (series). This could cause the appearance of a sub-harmonic one octave below the nominal pitch of the sound due to the period of the combined waveform taking twice as long as a single waveform would. Combining two non-resonant waveforms and a resonant waveform with a non-resonant waveform was possible. However, it was not possible to combine two resonant waveforms.  

How Does PD Synthesis Work?

Internally, phase distortion synthesis works by reading a sine wave table stored in memory. The most significant bits of an initial linear frequency counter are transformed into a secondary phase angle signal under envelope control. This signal reads the sine wave. Depending on the wiring, the transform will change with various wave shapes. Phase distortion synthesis is a subset of the Phase modulation synthesis. In addition, PM synthesis is the usual method of Frequency modulation synthesis within hardware synthesizers. Those two forms of audio synthesis are similar, but their implementation and the result are not equal. At phase modulation, an oscillator modulator can have its period. Phase distortion applies an angular modulator of straight-line segments hard synchronized to the same period as its corresponding carrier. Additionally, it modulates each cycle identically.   

Interactive Phase Distortion

After the CZ series of synthesizers in Casio`s VZ-1 synthesizer, a variation of PD synthesis was implemented and named “ Interactive phase distortion. “ This is an improved version of PD. It incorporated FM synthesis. Furthermore, it also had multiple oscillators combined in various configurable routing with the possibility to modulate each other using phase modulation or ring modulation.