Synth Overview

The Cosmo PD-101 is a phase distortion (PD) synthesizer inspired by the Casio CZ-101. It generates sound by warping the phase of an oscillator before sampling a base waveform, producing harmonically rich timbres from simple building blocks.

Signal Flow

MIDI Input (Note, Pitch Bend, Mod Wheel, Aftertouch, Velocity)
    │
    ▼
┌─────────────────────────────────┐
│  Modulation Sources             │
│  ├─ LFO 1 (sine/tri/sq/saw)   │
│  ├─ LFO 2                      │
│  ├─ Random Sample & Hold       │
│  ├─ ADSR Mod Envelope          │
│  ├─ Velocity                    │
│  ├─ Mod Wheel                   │
│  └─ Aftertouch                  │
└──────────────┬──────────────────┘
               │
               ▼
┌─────────────────────────────────┐
│  Modulation Matrix              │
│  (7 sources → 51 destinations)  │
│  Each route has adjustable depth│
└──────────────┬──────────────────┘
               │
               ▼
┌─────────────────────────────────────────────────┐
│              Voice (×8 polyphony)                │
│                                                  │
│  ┌───────────────┐  ┌───────────────┐           │
│  │   Line 1      │  │   Line 2      │           │
│  │ ┌───────────┐ │  │ ┌───────────┐ │           │
│  │ │ DCO Env   │ │  │ │ DCO Env   │ │           │
│  │ │ (8-step)  │ │  │ │ (8-step)  │ │           │
│  │ └─────┬─────┘ │  │ └─────┬─────┘ │           │
│  │       ▼        │  │       ▼        │           │
│  │ ┌───────────┐ │  │ ┌───────────┐ │           │
│  │ │Algorithm  │ │  │ │Algorithm  │ │           │
│  │ │(warp)     │ │  │ │(warp)     │ │           │
│  │ │ + DCW Env │ │  │ │ + DCW Env │ │           │
│  │ └─────┬─────┘ │  │ └─────┬─────┘ │           │
│  │       ▼        │  │       ▼        │           │
│  │ ┌───────────┐ │  │ ┌───────────┐ │           │
│  │ │Base Wave  │ │  │ │Base Wave  │ │           │
│  │ │(saw/sin/…)│ │  │ │(saw/sin/…)│ │           │
│  │ └─────┬─────┘ │  │ └─────┬─────┘ │           │
│  │       ▼        │  │       ▼        │           │
│  │ ┌───────────┐ │  │ ┌───────────┐ │           │
│  │ │ DCA Env   │ │  │ │ DCA Env   │ │           │
│  │ │ (8-step)  │ │  │ │ (8-step)  │ │           │
│  │ └─────┬─────┘ │  │ └─────┬─────┘ │           │
│  └───────┼───────┘  └───────┼───────┘           │
│          │                  │                    │
│          ▼                  ▼                    │
│  ┌───────────────────────────────────┐           │
│  │         Line Mixer                │           │
│  │  Normal / Ring Mod / Noise /      │           │
│  │  L1 / L1+L1' / L1+L2 / L1+L2'    │           │
│  └───────────────┬───────────────────┘           │
└──────────────────┼──────────────────────────────┘
                   │
                   ▼
┌──────────────────────────────────────────────────┐
│              Output Stage                         │
│                                                  │
│  ┌──────────┐ ┌──────────┐ ┌──────────────────┐ │
│  │ Volume   │→│ FX Chain │→│  Soft Clip (tanh) │ │
│  │ + Mod    │ │ 6 slots  │ │  → Audio Out      │ │
│  └──────────┘ └──────────┘ └──────────────────┘ │
└──────────────────────────────────────────────────┘

Phase Distortion — How It Works

In a traditional oscillator, a waveform is generated by stepping through a wavetable at a rate determined by pitch. Phase distortion adds a warping function between the phase accumulator and the wavetable lookup.

Normal:     Phase → Wavetable → Output
PD:         Phase → [WARP ALGORITHM] → Wavetable → Output

The warp algorithm reshapes the phase curve, which changes the harmonic content of the output in real time. Different algorithms produce different timbral characters — from subtle warmth to extreme metallic textures.

The Two Oscillator Lines

The PD-101 has two independent oscillator lines, each with:

Its own phase distortion algorithm (from 25 options)
Three 8-step envelopes controlling:
- DCO (Digitally Controlled Oscillator) — pitch
- DCW (Digitally Controlled Waveshaper) — warp depth
- DCA (Digitally Controlled Amplifier) — volume
Independent pitch, detune, and octave settings
A base waveform selector (sine, cosine, triangle, saw, square)

The two lines can be mixed using the Line Select control: L1 only, L2 only, L1+L2 (additive), L1+L1' (with L1's secondary algorithm), or L1+L2' (with L2's secondary algorithm).

Key Concepts

Term	Meaning
DCO	Digitally Controlled Oscillator — sets the pitch/frequency
DCW	Digitally Controlled Waveshaper — controls the warp amount
DCA	Digitally Controlled Amplifier — controls the amplitude
Algorithm	The mathematical function that warps the phase
Envelope	An 8-step step-function controlling a parameter over time
Modulation Matrix	Routes any of 7 sources to any of 51 destinations
FX Chain	6 serial effect slots processing the final audio

Performance Specs

Spec	Value
Polyphony	8 voices (SIMD-4 batched)
Audio Backend	Web Audio API (AudioWorklet) / CPAL (native) / nih-plug (plugin)
Wasm Binary Size	~200 KB gzipped
Sample Rate	44.1 kHz / 48 kHz
Latency (native)	10–30 ms (platform-dependent)

Next: Oscillators → | Algorithms → | Envelopes →

ON THIS PAGE

Synth Overview#

Signal Flow#

Phase Distortion — How It Works#

The Two Oscillator Lines#

Key Concepts#