CrispyZebra is a lightweight, high-performance C++ synthesizer core engine designed to replicate the Phase Distortion (PD) synthesis of the 1980s CZ-series synthesizers.

Live Demo

https://hugelton.github.io/CrispyZebra/wasm

The interactive WebAssembly (WASM) implementation with a full GUI is available.

Features

• Authentic PD Synthesis: Reproduces the Phase Distortion waveforms including Saw, Square, Pulse, Double Sine, Saw-Pulse, and Resonance windows (Saw, Triangle, Trapezoid).
• 8-Stage Envelopes: Three independent 8-stage EGs (DCO, DCW, DCA) per voice, fully compatible with vintage hardware SysEx point systems (Sustain/End points). DCA output can remain linear or use a selectable pseudo-exponential response for CZ-style loudness experiments.
• Fixed-Point Math: Designed with platform-independent integer arithmetic (int32_t / Q16) for minimal CPU overhead.
• WASM & Embedded Ready: Zero external dependencies (header-only wrapper ready). Suitable for both browser-based execution and microcontrollers.
• Modulation & Master Section: Built-in Vibrato LFO, Detuning, Key Follow (DCA/DCW), Ring Modulation, Noise Modulation, Portamento, and Master Drive/Pan controls.

Code Architecture

The engine is structured within the CrispyZebra namespace:

• Oscillator: The core Phase Distortion engine utilizing a custom Sine Look-Up Table (LUT) to warp phases dynamically.

  

• Envelope: High-precision Q16 internal state envelope generator supporting up to 8 stages with rate/level configurations.

• LFO: Low-frequency oscillator providing Triangle, Square, Saw Up, and Saw Down shapes for pitch modulation.

  

• Voice: A polyphonic container that couples two parallel lines (Oscillators) with routing, detuning, and modulation options.

• Engine<MaxVoices>: The template-driven master class that handles MIDI inputs (midiNoteOn / midiNoteOff) and renders block buffers. The default WebAssembly build intentionally uses Engine<8> in all line-select modes; two-line patches are not reduced to four voices.

Quick Start

CrispyZebra is a single-header engine. Include CrispyZebra.h into your project.

#include "CrispyZebra.h"

// Prepare your Sine Look-Up Table
const int16_t my_sine_lut[2048] = { /* pre-calculated sine values */ };

// Instantiate the engine with 8-voice polyphony
CrispyZebra::Engine<8> synthEngine;

void initAudio() {
    uint32_t sampleRate = 44100;
    synthEngine.setup(my_sine_lut, 2048, sampleRate);
}

void processAudio(float* buffer, uint32_t numSamples) {
    // Render stereo float samples directly into your audio callback
    synthEngine.processBlock<float, true>(buffer, numSamples);
}

void onMidiEvent(uint8_t status, uint8_t note, uint8_t velocity) {
    if (status == 0x90 && velocity > 0) {
        synthEngine.midiNoteOn(note);
    } else if (status == 0x80 || (status == 0x90 && velocity == 0)) {
        synthEngine.midiNoteOff(note);
    }
}

Web Build Sample Rate

The WebAssembly build defaults to 44.1 kHz, but the default engine rate and the browser AudioContext request can be selected at build time:

cd wasm
make SAMPLE_RATE=48000

Browsers may still choose the hardware output rate, so the engine is initialized with the actual AudioContext.sampleRate after startup.

Related Projects

• PicoCZ: A hardware port of the CrispyZebra engine optimized for the RP2040 (Raspberry Pi Pico) microcontroller.

License

This project is licensed under the GNU General Public License v3.0 (GPL-3.0) - see the LICENSE file for details. Copyright (C) 2026 Leo Kuroshita (@kurogedelic)

Disclaimer

CrispyZebra is an independent open-source project developed by Leo Kuroshita. It is not affiliated with, endorsed by, or associated with CASIO Computer Co., Ltd. in any way. "CZ-101", "CZ-series", and "Phase Distortion" are referenced solely for historical and educational compatibility purposes.