CHORDS for the M-VAVE FM-1

Custom firmware that turns the FM-1 into your Chord Generator web app. Pick a scale and a root: the white keys play the scale's chords (I, ii, iii… on up the keyboard), the black keys play its notes. Same twelve synth sounds, same voicings (dyads to 11ths), HOLD, the arpeggiator, the bass and the whole effects chain, running on the FM-1 itself.

It is built on FoMni's copy of the community FM-1 platform (Felucca by way of X0X): the hardware layer, USB, storage, safe mode and the installer are theirs, unchanged. The instrument and the UI are new.

Status: not yet run on a real FM-1. It builds and passes every test in the simulator (the whole app, UI and sound, on a computer) and in the browser emulator, but the device build and a hardware test are still to do. See "Safety" before installing.

From the web app to the FM-1

Web app	FM-1
Chord pads (I, ii, iii…)	White keys: one chord per key, 16 of them, so the scale repeats an octave up
NOTES tab	Black keys: the scale's notes, an octave above the chords. REC swaps the rows
HOLD button	PLAY (lit while on)
Arpeggiator mode	ARP turns it on and off; mode, rate, tempo and gate on the Arp page (SEQ)
—	Arp mode Melody: the chord plays, with a generated phrase over it; the Melody page (EDIT from Arp) sets it
Scale / Root / Instrument	SELECT / ALGORITHM / PRESETS encoders
Octave	OCT− / OCT+
Voicing, ATK, REL	Play page (HOME), knobs 1–3 (knob 4: level)
Bass mode / tone / volume	Bass page (EDIT from HOME, twice)
Reverb, Delay, Chorus, Tremolo	Effects page (FX)
Low-pass, High-pass, Auto-filter, Vibrato	Filter page (SEL)
Overdrive, Bitcrush, Waveshape, Compressor	Drive page (EDIT)
—	Setup page (GLO): arp octaves, tune, MIDI out, key lights
—	ENV held with a chord key: one more note
—	LFO held: chords play single notes (their root); press it twice quickly to lock single notes on (LFO lights), twice again for chords
—	SAVE saves; it also saves by itself when quiet

MIDI: notes in (USB or the TRS jack) play the current sound; chords and notes go out on channel 1, the bass on channel 2.

The melody generator

Set the Arp mode to Melody (Arp page, KNOB 1; ARP then turns it on and off). Holding a chord plays the chord, and over it, an octave up by default, a phrase of 1, 2 or 4 bars at the arp's rate, repeating. The phrase is written in scale steps over the chord's root, so it follows your chord changes: on the beats it lands on chord tones, between them it walks the scale, and it ends on the root. Each bar after the first repeats the first with its end varied. It keeps its place when you change chords; it starts from the top after you let go of everything.

Three pages shape it (EDIT from Arp):

Page	KNOB 1	KNOB 2	KNOB 3	KNOB 4
Melody: phrase	Density (how many steps get a note)	Length (1, 2, 4 bars)	Variation (how much of each later bar is rewritten; 0: exact repeats)	New (turn: a new phrase)
Melody: shape	Leaps (steps along the scale, or jumps)	Contour (Free, Rising, Falling, Arch, Valley)	Syncopate (notes moved off the beat, held across it)	Ends on (Root, Third, Fifth, Free)
Melody: voice	Volume (its own; 70 % matches the chord)	Octave (−1 to +3 over the chord)	Swing (50 % straight to 75 %)	Gate (note length)

Changing the phrase or shape settings keeps the phrase's character (the same seed); New rolls another. Volume, Octave, Swing and Gate change how it plays, not the phrase. Everything is saved with your settings.

What is different

• The 40 "♪" General MIDI sampled instruments are not included. In the web app they are soundfont samples downloaded from the internet as you pick them; the FM-1 has no connection and far too little memory for them. The 12 synthesized sounds are all here, with the web app's settings.
• The reverb is a Dattorro plate (FoMni's) standing in for Tone.js's Freeverb, at a similar size.
• The delay is an 8th note at the Tempo (the web app's was fixed at 120 BPM's 8th) and uses one line for both sides, to fit the FM-1's RAM.
• Vibrato bends the oscillators directly instead of going through a delay line (same rate and depth).
• Organ, Brass and Strings have their own sounds. In the web app all three were the same detuned sawtooths. Here the Organ is drawbars with a percussion, Brass a filter that opens as the note speaks (with a scoop into the pitch), Strings soft, dark sawtooths that swell in with a vibrato. Brass and Strings keep a minimum attack, whatever ATK is set to.
• Triangle is a 4-bit stepped triangle, as on game consoles. A smooth triangle sounds almost like the sine on the FM-1's speaker.
• CPU guard: if the audio load passes 85 %, CHORDS plays fewer voices at once (down to 4), and gives them back when the load drops. With every effect on and 12 Strings voices, the load is about 1.5× FoMni's heaviest; most settings are well under it.

Try it first, in the browser

web/emu/ builds the whole firmware for the browser (the same C code, with sound). The GitHub build below publishes it, or build it yourself (web/emu/build.sh, see the script).

Build and install

The device build needs JieLi's Linux toolchain and three files from their SDK, which the build fetches from their servers. The simplest way, from a phone or any computer:

1. Put this folder in a new GitHub repository (it already contains .github/workflows/build.yml).
2. In the repository: Settings › Pages › Source: GitHub Actions.
3. Push (or Actions › build › Run workflow). It builds the firmware, runs the tests, and publishes a site with the emulator, the web installer and the .fwsc download.
4. Open the site's Install page in Chrome or Edge with the FM-1 connected by USB. On Android, Chrome with a USB-OTG cable works for Web MIDI.

The version number is in the VERSION file: change it with each update so the installer and the FM-1 show which one you have.

Locally instead: see BUILDING.md (./build.sh, then python3 tools/fm1_install.py build/chords.fwsc).

Safety

Installing custom firmware is at your own risk. The platform has the community's safety nets: the installer can put M-VAVE's own firmware back; after two failed starts CHORDS stays in a safe mode with USB on so the installer can still reach it; holding OCT− and OCT+ for 5 seconds enters update mode; and tools/fm1_rescue.sh / FM-1-transporter cover the chip's own update mode. M-VAVE's M-UPGRADE also restores stock firmware.

Tests

tests/run_tests.sh runs the platform tests, and the whole app in the simulator: tests/scenarios/chords.omni (keys, chords and their notes, HOLD, ARP timing, bass, layout swap, scales, roots, saving), sounds.omni (every sound and every effect, levels) and heavy.omni (12 voices with all effects, and the CPU guard). Screenshots and audio land in build/scenarios/.

Licence

GPL-3.0-only, as the platform it is built on. See LICENSING.md.