opl-audio

Pure-Rust OPL2 (Yamaha YM3812) and OPL3 (YMF262) FM song renderer.

Renders a list of timed MIDI events against a bank of AdLib FM patches to PCM audio through an original YM3812 emulator. The crate is engine-agnostic: it knows MIDI and FM synthesis — not any specific game, sound driver, or file format. Callers load their own instrument bank (from a .bnk or anywhere else) and feed timed events; the crate returns mono (OPL2) or stereo 18-channel (OPL3) PCM.

• #![forbid(unsafe_code)]
• Single dependency: thiserror
• Register tables are derived from the published OPL2 formulas — no copyleft emulator source is used, so the crate is cleanly licensable under MIT OR Apache-2.0.

What it does

• OPL2 core — nine 2-operator channels, four waveforms, ADSR envelopes following the published rate table, key-scale rate/level, tremolo and vibrato LFOs.
• MIDI dynamics — note velocity, CC7 channel volume, CC11 expression, CC64 sustain pedal, ±2-semitone pitch bend, and channel-10 percussion (drum patches played as melodic voices keyed by note).
• OPL3 mode (render_stereo) — eighteen 2-op channels sharing the same operator pipeline, with CC10 pan quantized to hard L/C/R via the per-channel output-enable bits.

Usage

use opl_audio::{MidiMsg, OplBank, RenderOpts, TimedEvent};

let mut bank = OplBank::new();
bank.insert_program(0, my_patch); // an OplPatch you built or loaded from a .bnk

let events = vec![
    TimedEvent { delta_ticks: 0,  msg: MidiMsg::NoteOn  { ch: 0, note: 69, vel: 127 } },
    TimedEvent { delta_ticks: 96, msg: MidiMsg::NoteOff { ch: 0, note: 69 } },
];

// division = MIDI ticks per quarter note, bpm = tempo
let pcm = opl_audio::render(&events, &bank, 96, 120, RenderOpts::default())?;
// pcm.samples: Vec<f32> in [-1.0, 1.0] at pcm.sample_rate (49716 Hz by default)

For stereo OPL3 output, call opl_audio::render_stereo(..), which returns a StereoPcm { left, right }.

See examples/render_tone.rs for a complete, data-free example:

cargo run --example render_tone

Provenance

Extracted from the dm2-tools Dungeon Master II toolchain, where it renders the game's DOS AdLib soundtrack. The per-crate commit history is preserved from that monorepo.

License

Licensed under either of Apache License, Version 2.0 or MIT license at your option.