JAM-8 manual

A loop machine for the MMT-8

JAM-8 is a second firmware for the same hardware: the 8031 at 12 MHz, the 32 KB EPROM, battery RAM, one MIDI in, one MIDI out, the 16x2 LCD, the keys, and the LEDs. It plays loops and writes new patterns while it plays. It does not record songs. OpenMMT-8 does that. The key names here are the names printed on the panel.

This project is not affiliated with Alesis. A lane is one of the eight tracks. A lane has a role: DRUM, BASS, CHORD, or LEAD. A step is one position in a lane, and a lane has 1 to 64 steps. A scene is a set of eight lanes. There are 16 scenes. The chain is a list of scenes that plays in order.

Turn it on

Burn jam8_rom.bin to a 27C256 and swap it in. The build page has the steps. In the plugin, select Use built-in JAM-8 in the ROM menu.

The LCD shows:

Memory stays in the battery RAM. Hold ERASE at power-on to clear the memory. The LCD then shows MEMORY CLEARED and FACTORY SCENES. A first power-on does the same when the memory is empty or holds data from another ROM, including OpenMMT-8. Send an OpenMMT-8 dump before you swap chips if you want your songs back later.

Hold a function key to show its page. Release it to return home. While the key is held, PAGE UP and PAGE DOWN pick the field, + and − change the value, and the keypad enters a number. A number still being typed is set when the key is released. EDIT is different: a tap enters step edit, and another tap leaves it.

Pressing STOP while a function key is held returns home at once. That press does not start or stop playback. A STOP tap by itself still does.

Read the home screen

Line 1 is the style of the focused lane, the current chord (m is minor, o is diminished), and the focused track, T1 to T8. The tempo is on the TEMPO page. Hold TEMPO.

Line 2 is one character for each lane, then the place in the scene, then the scene number.

When a scene is queued, >02 shows the next scene. Otherwise, during play, 1.1 is the bar of the scene and the beat. S01 is the current scene. A message replaces line 2 for about 1 second.

Play

PLAY starts after a short pre-roll of about 40 ms. JAM-8 sends MIDI Start, Continue, Stop, and Clock when CLK OUT is ON.

Hold TEMPO for the tempo, 40 to 250 BPM, and a fine field of 0 to 9 tenths. Line 1 shows SYNC INT when the internal tempo runs the clock, and SYNC EXT when the clock source is MIDI. With SYNC EXT the tempo comes from the incoming MIDI clock, and the value here is kept for when the source goes back to INTERNAL. + and − on the home screen change the tempo by 1 BPM. They do nothing when the source is MIDI.

Hold CLICK and set CLICK to ON to hear a click on each beat during play.

While it plays

These gestures work from the home screen.

• Tap a track key to focus that lane and mute or unmute it. Tap several track keys together to mute or unmute them all at once.
• Hold a track key longer than 300 ms to focus the lane without changing its mute.
• Hold QUANT and hold a track key. That lane drops out while both keys are held. Release either key and it plays again on its next step. The stored mute does not change.
• Hold LOOP and tap a track to latch or unlatch solo. Several lanes can be latched. The last one clears solo.
• Hold LOOP and a track past 300 ms to solo only while the track is held. Release the track keys and the latch is unchanged.
• Hold a track key, then + or −, to change that lane’s density from 0 to 9. On a lane with the EUCLID style, this changes Euclid K.
• REW or FF rotates the focused lane by one step.
• Hold LOOP and press REW for a 1/8 (2-step) beat-repeat stutter, or FF for a 1/16 (1-step) roll, while held.
• Keys 1 to 9 queue scenes 1 to 9. 0 queues scene 10.
• Hold FOOT or FILTER for a fill. Drum lanes play their fill steps.
• Tap MERGE to mutate the focused lane: a new seed and a new pattern.
• Hold MERGE and press + to mutate. Hold MERGE and press − to step back through the seed history. The last 8 seeds are kept.
• Hold MERGE and tap a track to mutate that lane. Hold MERGE and press REC to mutate all non-captured lanes except lane 1, the kick, at once.
• Hold COPY and press MERGE to save a snapshot of the current scene. Hold ERASE and press MERGE to reload it.
• ECHO turns MIDI thru on or off. With ECHO on, MIDI in passes thru to the channel of the focused lane.

A stored mute, and a latched solo, wait for the launch point on the QUANTIZE page. A dropout and a held solo cut notes that are already sounding. A queued scene starts at the end of the current scene’s bars. A scene change clears a latched solo. When stopped, mutes and a latched solo change at once.

The track LEDs are lit when the lane is audible. They blink fast while a mute or solo change is waiting, and slowly when the lane is armed for capture. PLAY is lit while playing. REC is lit when a lane is armed. PART blinks while a scene is queued. SONG is lit when the chain is on. EDIT is lit in step edit. ECHO is lit when MIDI thru is on. LOOP flashes on each beat during play.

Change a pattern

Hold TAPE. That is the GEN page. A change to STYLE, SEED, DENSITY, or the Euclid fields writes a new pattern. The new pattern starts at the next loop of the lane.

Styles by role:

• DRUM: HOUSE, TECHNO, BREAKS, BOOMBAP, GARAGE, DEMBOW, TRAP, ELECTRO, EUCLID.
• BASS: ROOT 8, OFFBEAT, OCTAVE, ACID, WALK, EUCLID.
• CHORD: STAB, PAD, STRUM, EUCLID.
• LEAD: ARP UP, ARP DOWN, ARP UPDN, ARP RAND, CONVERGE, CHORD, TURING, EUCLID.

Hold LENGTH for the length of the lane.

Hold CHAN for the lane’s voice. A new role resets the lane. CHANNEL is 1 to 16. NOTE is the drum note, or the base note of a melodic lane, from C-1 to G9. VOICES is 3 or 4 notes in a chord. SEVENTHS and HARMONY are OFF or ON. TRANSP is −24 to +24 semitones. SPREAD ON is a Drop-2 open voicing: it raises the second chord voice by an octave.

MOD CC, OFF or 1 to 119, sends that MIDI CC before each note on the lane’s channel, using the step velocity or accent. When it is 65 (Portamento Switch), JAM-8 sends 127 on tied steps and 0 otherwise.

On the home screen the CC knob sets the focused lane’s density. Set the controller on the NAME key, the KNOB page: KNOB CC is OFF or 1 to 119. On a page the knob sets the current field. The knob CC does not pass thru.

Steer the harmony

Hold TRANS. Line 1 shows the current chord. Chord lanes move each voice to the nearest note of the next chord.

A keyboard on the control channel steers the harmony. Notes on that channel are not captured and do not pass thru.

• CTRL BY KEY: a note sets the key. The progression continues in the new key.
• CTRL BY CHORD: a single note in the scale sets the scale-degree chord. A single note outside the scale is ignored. Holding 2 or more notes at once detects the chord you played, including borrowed and chromatic chords, sus4, and maj7, and voice-leads the chord lanes to those tones. The chord holds until the next control note or a change on the HARMONY page.

The change waits for the launch point. Hold QUANT and set LAUNCH to STEP, BEAT, or BAR. That is when mutes and control-channel changes take effect. SWING is 50 to 75% and swings the 1/32, 1/16, and 1/8 steps.

Capture what you play

1. Hold REC and press a track key. The lane shows R. Its LED blinks slowly. A tap of REC arms or disarms the focused lane.
2. Play notes at MIDI in. Each note goes on the nearest step. On a CHORD lane, up to 4 notes played on the same step are captured as a chord. When LAUNCH is STEP, a timing offset of 0 to 15 ticks is captured, and a note held into the next step sets TIE.
3. After one loop of the lane, capture stops. When you arm capture while stopped, it starts with PLAY.

A captured lane keeps its notes. EVOLVE and the generator do not change it. A change to STYLE, SEED, DENSITY, or the Euclid fields writes a new pattern on it again.

Edit a step

Tap EDIT. During play the step under the playhead blinks. In step edit the track LEDs show the steps of the page.

Line 1 is the track, the page of 8 steps, the selected step, and * when the step is on (− when off). Line 2 is the field of the selected step.

• Tap a track key to turn that step on or off. Press a track key to select the step.
• Hold a track key, then 1 to 4, to set the ratchet of that step. Hold a track key, then + or −, to change the field of that step.
• REW and FF move by a page of 8 steps. PAGE UP and PAGE DOWN pick the field. + and − change the selected step.
• On a melodic lane, 1 to 8 set the scale degree. On a drum lane, the digits enter the MIDI note.

Conditions are ALWAYS, FILL, NOT FILL, 1 OF 2, 2 OF 2, 1 OF 4, 4 OF 4, and FIRST. FILL plays only during a fill. NOT FILL plays only without a fill. 1 OF 2 plays on the first of every 2 loops. When the previous step had PROB under 100%, 1 OF 2 plays only if that step fired, and 2 OF 2 plays only if it skipped. 1 OF 4 plays on the first of every 4 loops. 4 OF 4 plays on the fourth. FIRST plays only on the first loop after PLAY.

An edited lane is a captured lane.

Scenes and the chain

Hold LOOP and set BARS from 1 to 16. A queued scene starts after these bars.

Hold PART and set SCENE from 1 to 16 to queue that scene. From the home screen, the number keys queue scenes 1 to 10.

Hold SONG for the chain. CHAIN is OFF or ON. The SONG LED is lit when the chain is on. POSITION is 1 to 32, the entry you are editing. SCENE is END or 1 to 16. END stops the chain list there. REPEATS is 1 to 16. After the last entry the chain starts again at entry 1. PLAY with the chain on starts from the first chain entry.

Hold COPY. Press REC to copy the current scene to TO SCENE. Press a track key to copy the focused lane to that lane. Hold ERASE. Press REC to erase the current scene. Press a track key to erase that lane.

Clock, the factory set, and the dump

Hold CLOCK. SOURCE is INTERNAL or MIDI. MIDI follows MIDI Clock, Start, Continue, and Stop at MIDI in. Incoming clock jitter passes through. CLK OUT is OFF or ON. With CLK OUT ON and SOURCE INTERNAL, JAM-8 sends MIDI Clock, Start, Continue, and Stop.

A first boot, or a cleared memory, loads these factory settings: tempo 124.0, swing 54%, key A, scale MINOR, progression i VI III VII, control channel 1, CTRL BY CHORD, CLK OUT ON, LAUNCH BAR, 4 bars per scene. Drum lanes are on channel 10, bass on channel 2, chords on channel 3, lead on channel 4. CHAIN is OFF.

The factory chain is scene 1 two times, scene 2 two times, scene 1 two times, scene 3 four times.

To send every scene over MIDI:

1. Hold CLOCK.
2. Press PAGE DOWN until DUMP shows.
3. Press REC, still holding CLOCK. The LCD shows SENDING DUMP, then DUMP SENT.

The dump holds the settings, the 16 scenes, and the chain. It takes about 24 seconds. Playback stops during a dump. The header is F0 7D 4A 38 01.

To load a dump, send it back to MIDI in. The LCD shows RECEIVING DUMP, then DUMP LOADED. DUMP ERROR means the data was not complete. After a dump error, the next power-on loads the factory scenes.

Inside

The source is in jam8/core/, in C for SDCC’s small model. The development notes are in jam8/README.md.

• Timer0 runs at 96 ticks per beat of the internal tempo. With MIDI clock in, each F8 gives 4 ticks.
• Each lane works out its step ahead of time. Lane l does so 8 − l ticks early, so the eight lanes do their work on eight different ticks and the notes still leave on their tick.
• The event queue has 32 entries with absolute due ticks. Due note-offs go out before due note-ons.
• Outgoing F8 clock takes priority in the UART transmit interrupt, ahead of queued channel messages.
• Voice leading for a 4-voice chord is worked out in background passes.
• In the timing scenario at 124 BPM, kick to kick measured 181 to 182 blocks of 2.67 ms, against 181.5 nominal.
• Most locals are static __xdata, because internal RAM is 128 bytes. The hot paths avoid SDCC’s 16-bit library calls for % and *.
• 16 scenes of 0x900 bytes live at 0x2000–0xAFFF in battery RAM, with the chain at 0xB000. The settings page carries a magic byte and a JAM8 signature.

The source of this text is jam8/MANUAL.md in the repository.