# DOA303 — modified acid bass synthesizer

An original TB-303-inspired monosynth by **Design On Acid**, built with C++17 and JUCE 8.
VST3, Audio Unit (macOS), and standalone. No samples or commercial plugin code.

![DOA303 interface](screenshot.png)

## Version 1.1.2 — official DOA logo and two sound improvements

1. **Accent circuit response.** Separate charge and sweep capacitors retain energy between
   accented triggers. Resonance changes the sweep attack/release, giving repeated accents a
   rising, rounded response. Slides still tie notes without retriggering the envelopes.
2. **Oversampled overdrive with tone.** Asymmetric saturation, continuous clean-to-driven
   blending, gain compensation, and a dark-to-open tone control run inside the 4x engine.
   A 129-tap Blackman-windowed sinc replaces box averaging and filters the complete nonlinear
   signal before downsampling. Drive and tone changes are smoothed; Drive=0 bypasses coloration.
   The plugin reports the FIR's 16-sample latency to the host.

The new hardware-inspired panel uses charcoal metal, blue-grey silkscreen, recessed knobs,
red pointers/LEDs and tactile sequencer keys. The supplied TD-3-MO image informed the palette
and hierarchy; the interface is drawn natively, without embedding the product photo or logos.

## Instrument

- PolyBLEP saw/square oscillator; coupled diode ladder low-pass and resonance-loop high-pass
- Filter envelope, accent, exponential slide, overdrive and output volume
- 16 steps with pitch, octave, gate, accent and slide; length 1–16, transpose ±12
- Host transport sync; **RUN** uses the internal tempo when the host is stopped
- MIDI mode: last-note priority, overlapping notes slide, velocity ≥100 accents
- Musical randomizer and clear; patterns and sound controls save with the DAW project
- Knob values are editable; double-click restores the parameter default

The plugin is now named **DOA303**. Manufacturer/plugin codes and existing parameter IDs
are retained, as is the legacy `SquelchState` state root for saved-state compatibility.
The macOS bundle identifier changes to `com.designonacid.doa303`. Rescan after replacing
older Squelch binaries; host-specific migration of existing sessions has not been verified.

Download ready-to-install packages from the [latest release](https://github.com/designonacid/DOA303/releases/latest).

## Build and install

Requirements: CMake 3.22+, C++17 compiler (Xcode on macOS, Visual Studio 2022 on Windows).
JUCE 8.0.4 is fetched automatically; alternatively pass `-DJUCE_DIR=/path/to/JUCE`.

```sh
cmake -B build -DCMAKE_BUILD_TYPE=Release -DDOA303_BUILD_TESTS=ON
cmake --build build --config Release --parallel 4
ctest --test-dir build -C Release --output-on-failure
```

Outputs: `build/DOA303_artefacts/Release/{VST3,AU,Standalone}` (some generators omit `Release`).
Copy `DOA303.vst3` to:

- macOS: `~/Library/Audio/Plug-Ins/VST3/` (AU: `DOA303.component` → `~/Library/Audio/Plug-Ins/Components/`)
- Windows: `C:\Program Files\Common Files\VST3\`
- Linux: `~/.vst3/`

Rescan your DAW, load **DOA303**, then start host playback or press RUN.
Builds are unsigned. GitHub Actions builds Windows, universal macOS and Linux artifacts on push;
download them from the repository's [Actions page](https://github.com/designonacid/DOA303/actions).
Artifacts include this license and third-party notices.

## Validation and research

`tests/dsp_test.cpp` checks finite/bounded output at 44.1/48/96 kHz, both waveforms, extreme
settings, clean bypass, audible tone response, accent response, deterministic reset and release.
`DOA303SmokeTest` checks the real processor, MIDI, sequencer, latency and state recall; it writes
`plugin_render.wav` and a 2x `ui.png` snapshot when run in a GUI-capable desktop session.
`tests/render_demo.cpp` renders an eight-bar example without JUCE.

See [research notes](docs/EMULATION_RESEARCH.md) for sources, implementation choices and limits.
These are behavioural models. No claim of matching ABL3, Phoscyon or a measured TB-303 is made.

## Creative Commons

Original DOA303 source, interface artwork and documentation are dedicated under
**Creative Commons CC0 1.0 Universal**, to the extent of the author's rights. See [LICENSE](LICENSE).
Attribution to Design On Acid is appreciated but not required. The reference product photo is
not distributed. Third-party trademarks are used only for descriptive comparison.

JUCE and its dependencies retain their licenses; CC0 does not relicense them. JUCE 8.0.4 offers
AGPLv3 or commercial terms. Distributing a combined plugin under JUCE's AGPL option requires
compliance with AGPLv3, including corresponding source. See [THIRD_PARTY_NOTICES.md](THIRD_PARTY_NOTICES.md).