Definition
Phase distortion (PD) is the technique introduced by Casio with the CZ series (CZ-101 in 1984, then CZ-1000, CZ-3000, CZ-5000, CZ-1). A sine wave is read from a table at variable speed within each cycle: if the first half of the cycle is read faster and the second more slowly, the sine is deformed into a wave rich in harmonics (similar to a sawtooth). The amount of distortion is controlled by the DCW (Digitally Controlled Wave), which with its envelope behaves much like a filter opening.
Structure of a CZ
- DCO (digital oscillator) with 8 waveforms: sawtooth, square, pulse, double sine, saw-pulse and three “resonant” shapes (resonance I, II, III) that imitate a resonant filter opening.
- DCW: depth of the phase distortion (0 = pure sine); with its 8-stage envelope.
- DCA: amplifier with an 8-stage envelope.
- Two lines (line 1 and line 2) that can be combined, with ring modulation and noise modulation; detune between the lines for thickness.
- The 8-stage envelopes (rate and level) with sustain and end points allow complex movements, far more articulated than an ADSR.
PD vs subtractive
- The DCW has no true resonance: the “resonance” shapes simulate it with a wave that contains a moving peak of harmonics. The result recalls a resonant filter sweep but with a digital, clean, “glassy” character.
- There is no analog filter, so no filter saturation: the sound stays glossy even with the DCW closed. Many modern emulations add filters anyway.
Typical sounds
- Clean, defined basses (saw with the DCW closing in 150–300 ms): excellent for house, electro, synthpop.
- “Fake” resonant sweeps (resonance shape + long DCW envelope): digital acid character.
- E-pianos and bells with double sine and ring modulation between the lines.
- Pads with two detuned lines and multi-stage envelopes.
- Digital brass of the '80s.
Instruments
CZ V (V Collection 9) emulates the CZ-101/CZ-5000 with additions (modulations, effects). For PD the main options are CZ V and some modern synths with a “phase distortion” mode (for example the warps of Vital and Serum, and Arturia Pigments, allow similar phase deformations).
Example in A minor
House bass at 122 BPM in CZ V: line 1 saw, DCW 70% falling to 20% in 200 ms, DCA with 400 ms decay; line 2 an octave below with square wave, detune +6 cents. Line A1 – A1 – C2 – E1 offbeat between the kicks; EQ with HP at 35 Hz and a small boost at 900 Hz for presence. Am7 – Dm7 chord stabs with “resonance II” shape and very fast DCW envelope: a sound reminiscent of late-'80s house.
Common mistakes
- Looking for the “fatness” of a Minimoog: the CZ gives precision and gloss, not saturation. Add a saturator if you need warmth.
- 8-stage envelopes programmed at random: start with 3–4 stages and add only if needed.
- Forgetting velocity → DCW: it is the simplest way to make the sound expressive.
Exercise
- In CZ V create the same bass with fixed DCW and with enveloped DCW: compare the “vocal” effect.
- Recreate with the resonance shape an acid sweep on a sixteenth-note line in A minor (A1 A2 C2 A1 G1…).
- Compare the same pluck made in CZ V and in a subtractive synth (Mini V): describe the difference in the spectrum.
Connections
“Subtractive synthesis”, “FM synthesis”, “Filters”, “Sync and ring modulation”, “Envelopes, LFOs and modulation”.