The Mega Drive / Genesis sound chips as a synth, on the M-VAVE FM-1.

Hear a sample: a new song recorded from an FM-1 running OPN-1, with instruments from Sonic the Hedgehog

OPN-1 is open-source firmware for the M-VAVE FM-1 keyboard. It runs accurate recreations of the console's two sound chips, the Yamaha YM2612 (six FM channels plus a sample DAC) and the SN76489 PSG (three square waves and a noise channel), and turns them into a synth you play from the FM-1's own keys and knobs, or over USB MIDI.

It holds a library of 128 FM patches in 4 banks of 32, like the FM-1's own firmware. The library starts empty: a companion web app fills it from VOPM .opm patch files, or pulls the instruments out of a game's VGM music, and lets you edit, audition and organise them. The same app can stream the original songs to the FM-1 and play them back exactly, with a live view of every channel on the device's screen.

The FM-1 play screen: patch B1 04, its algorithm and the sound knobs The four operators' envelopes SEQ: every channel's note, level and patch

Still on OPN-1 1.x? The web app above needs 2.0. The 1.0 page stays at https://opn-1.putch.co.uk/v1/, and 1.0.0 is on the releases page. Installing any version is at your own risk: see the disclaimer.

Features

Accurate chips. The YM2612 core is a C port of Aaron Giles' ymfm and matches it sample for sample in the tests; the PSG is a port of MAME's Sega PSG and matches it tick for tick. Both run in real time on the FM-1's CPU.
A patch library. 128 slots in 4 banks of 32, kept in flash. PRESETS on the FM-1 steps through them and a MIDI program change picks one. Fill them from .opm banks (the VOPM format, as in the 2612.org packs) or from a game's VGM songs, into whichever bank and slot you pick, and export a bank back to .opm.
Single, Layer or Split. Out of the box the FM-1 plays the selected patch, up to six notes at once. Layer stacks up to six patches on the keys, each at its own volume and playing with the note, after a delay or on release (an attack, a body and a tail). Split gives each MIDI channel its own patch, for a sequencer.
Edit on the device or the page. Knob pages for the sound, each operator's tone, all four envelopes drawn, the LFO, vibrato and a doubled detune, and an arpeggiator. The web app's editor shows every operator and envelope at once and plays changes as you make them. SAVE keeps the patch in its slot.
A game's drums and noise. VGM files give up their sampled drums and the shaped noise and square-wave sounds the game used, playable on channels 10 and 7 to 11.
Songs, streamed. Original VGM songs play on the FM-1 as the console played them, including DAC drums. Nothing is stored on the device: the page streams each song while it plays.
Songs as MIDI. The same songs can be turned into MIDI notes and patch changes in GenMDM's layout: played live on the FM-1 in GenMDM mode, or saved as a .mid file to open in a DAW. Close to the original, not exact.
See what a song does. SEQ shows every channel's note, level and patch in real time. REC grabs the sounds a song is playing right now, ready to play.
MIDI over USB or the TRS jack. By default the FM patch plays on channels 1 to 6 and 12 to 15, the square waves on 7 to 9, the drums on 10 and noise on 11. GenMDM's layout and control changes are a setting away.

New in 2.0

1.0 played the last set of sounds the page sent from a game's music. 2.0 makes the FM-1 a patch-based synth:

A library instead of one sound set. 128 patches in 4 banks of 32, picked with PRESETS or a program change. 1.0 kept only the last game's sounds; on upgrading, they move into bank 1.
.opm patches as well as VGM. Import VOPM banks (such as the 2612.org packs) into any bank and slot, and export a bank back to .opm.
Single, Layer and Split replace 1.0's POLY and one-channel modes: one patch, up to six stacked (with delay and release triggers), or one per MIDI channel.
A full patch editor. 1.0's editor set one FM channel's CCs; 2.0's draws every operator's envelope, edits a library patch and saves it back to its slot.
Redrawn FM-1 screens: all four envelopes, one operator at a time, the setup, and a cleaner SEQ.
Songs as MIDI: play a VGM song live in GenMDM mode, or save it as a .mid for a DAW.
A normal MIDI layout by default: the patch on channels 1 to 6 and 12 to 15. GenMDM's layout is still a setting.
The page checks the firmware: it works only with OPN-1 2.x. For 1.x, the 1.0 page stays at https://opn-1.putch.co.uk/v1/.

The FM-1's screens



HOME: the patch, its algorithm, the main knobs	EDIT: one operator, large. Again for the next	ENV: all four envelopes

LFO: rate, depths and which operators it moves	FX: vibrato and a doubled detune	ARP: the arpeggiator

GLO: velocity, bend range, MIDI mode, tuning	GLO again: SETUP, a layer's or split's parts	SEQ: every channel live

The web app

The Library: .opm patches imported, bank 1 on the FM-1

Library: import .opm banks or VGM songs, tick the patches, pick a bank and slot, and send them.

The Editor: a patch's algorithm and its four operators with their envelopes

Editor: pick a patch, change it and hear it on the FM-1 as you go, then save it to its slot.

The Setup tab: three patches layered, one after a delay and one on release

Setup: Single, Layer or Split. A layer stacks patches on the keys; a split gives each MIDI channel its own.

Getting started

Install the firmware on the FM-1, as in Installing the firmware below.
Open the web app in Chrome or Edge: https://opn-1.putch.co.uk/. To run it locally instead (Web MIDI needs https or localhost):
```
cd web && python3 -m http.server 8000          # then open http://localhost:8000/
```
Fill the library. In the Library, drop .opm files (or a few VGM or VGZ songs from one game), tick the patches you want, pick a bank and a start slot, and press Send to FM-1. OPN-1 does not include any game music or patches; use files you have the right to use.
Play. Turn PRESETS to step through the patches. The web app's Help tab explains every button and knob on the FM-1, and what to do when something goes wrong.

Rescue: if the FM-1 ever fails to start, hold OCT- while switching it on. It starts the USB updater only, so a working firmware can be installed from there.

Installing the firmware

You need the FM-1 plugged in over USB and Python 3. The commands below run from the OPN-1 project folder:

Get the project: Code > Download ZIP on GitHub and unzip it, or git clone https://github.com/putchdev/opn-1.git.
Download the .fwsc from the latest release into that folder. In the commands below, use the name of the file you downloaded.

Close anything else that talks to the FM-1 over MIDI first, including the OPN-1 page and any DAW. On Windows only one program at a time can use it.

Windows. Install Python from python.org, ticking "Add python.exe to PATH". Open Command Prompt in the project folder and run:

py -m pip install mido python-rtmidi
py tools\fm1_install.py opn1-2.0.0.fwsc

macOS. Install Python from python.org (or brew install python). Open Terminal in the project folder and run:

python3 -m venv ~/.venv/fm1
~/.venv/fm1/bin/pip install mido python-rtmidi
~/.venv/fm1/bin/python tools/fm1_install.py opn1-2.0.0.fwsc

Linux. On Debian or Ubuntu:

sudo apt install python3-mido python3-rtmidi
python3 tools/fm1_install.py opn1-2.0.0.fwsc

On other distributions, use the macOS commands (Python's venv module may be a separate package).

The installer asks before it writes anything. The FM-1 then restarts into OPN-1 and shows its version on the screen. tools/fm1_install.py --info shows what the connected FM-1 runs. If an install is cut off, run the same command again and it finishes.

To go back to the official firmware or another one, use the FM-1 Firmware Hub in Chrome or Edge.

Disclaimer

Installing OPN-1, or any custom firmware, on an M-VAVE FM-1 is done entirely at the owner's own risk. It may void the device's warranty, and an interrupted or faulty install could leave it unusable. OPN-1 is provided "as is", without warranty of any kind (see sections 15 and 16 of the licence). Its authors accept no responsibility or liability for any damage to, or loss of use of, any device, or for any other loss arising from installing or using it. If you are not comfortable with that, do not install it.

Built with AI

OPN-1 was developed with the help of AI: much of its code, tests and documentation were written by Claude (Anthropic) under the author's direction, then reviewed, tested on a real FM-1 and released by the author. It may still contain mistakes; reports and fixes are welcome.

Documentation


docs/MIDI.md	The full MIDI protocol: playing, setups, the library, songs as MIDI, streaming
docs/DEVELOPING.md	Building, the host simulator, the accuracy tests, the code's layout
docs/RULES.md	The FM-1 chip's rules and what the build checks for
docs/API.md	What the platform layer gives the app

Credits

OPN-1 stands on the work of others:

Dinghy by zvenson: the firmware base, host mode and build checks.
Felucca by Leo Kuroshita (Hügelton Instruments), with the changes of SLOOP by isod89: the FM-1 platform (boot, USB, updates, audio, panel).
ymfm by Aaron Giles: the YM2612 emulation that opn2.c ports.
MAME's sn76496 by Nicola Salmoria and others: the PSG that psg.c ports.
Nuked-OPN2 by Nuke.YKT: a second reference in the tests.
GenMDM: the MIDI layout OPN-1 follows.
The Terminus font by Dimitar Zhekov.

Licence

GPL-3.0-only: you may use, study, change and share OPN-1, and whoever receives a firmware built from it must be able to get its source. Third-party parts keep their own licences; see LICENSING.md.

OPN-1 is an independent project. It is not made, endorsed or supported by SEGA, Yamaha, M-VAVE, or the authors of the projects above. Sega, Mega Drive and Genesis are trademarks of SEGA Corporation; M-VAVE and FM-1 belong to their owners.