LJam Docs

1. What is LJam

LJam is a browser-based loop sequencer with a 6-track grid interface. It uses Tone.js for built-in synthesis and supports Web MIDI output so you can drive external instruments and DAWs directly from the browser.

Six tracks are arranged in a 3×2 grid: two drum panels and four melodic synth panels. Each track has 10 slots and 8 chains for building arrangements on the fly.

2. Getting Started

1. Open the app — click anywhere or press Space to start the audio engine.
2. Click cells in any grid to add notes.
3. Press Space (or the play button) to hear your loop.

Each grid panel has its own instrument. Drum panels let you toggle individual hits; melodic panels let you draw notes with variable length.

3. The Grid

The interface is a fixed 3×2 layout of grid panels. Each panel is 32 steps long (two bars of 16 sixteenth notes).

If bar 2 (steps 17–32) is empty for a track, the playhead loops at step 16 for that track.

4. Editing Notes

Drum Grids

• Click an empty cell to toggle a hit on.
• Click an active cell to toggle it off.
• Click + drag across cells to paint or erase in one gesture. In stamp mode, hits are spaced to the stamp duration grid.

Melodic Grids

• Click + drag horizontally on an empty area to draw a note. The drag distance sets the note length.
• Click the note head (left edge) to select it:
  • Drag right to resize the note.
  • Click the head again (without dragging) to delete the note.
• Click the note body or tail to trim the note end back to that step.
• Arrow keys — with a note selected, press ↑ / ↓ to move it to an adjacent pitch row.

5. Slots (A–J)

Each track has 10 independent slots labeled A through J. Think of them as pattern variations for a single track.

• Click a slot button to select it for editing — the grid loads that slot's data.
• Click again (on the already-selected slot) to queue it for playback. Double-click and right-click also queue.
• A queued slot switches in at the next loop boundary (step 1 or step 17).
• When playing a single slot (no chain), the slot button shows a solid fill. When a chain is active, the currently playing slot shows a small colored dot instead.
• Slots with data show a filled indicator; empty slots appear dimmed.

6. Chains (1–8)

Chains let you sequence slots into longer patterns. Each track has 8 chains.

• Click a chain button (1–8) to select it for editing.
• Click again (on the already-selected chain) to activate/deactivate it. Double-click also works as a shortcut.
• When a chain is active, its button shows a solid fill.
• Press the + button to append the current editing slot to the selected chain.
• Click a slot tag inside the chain display to remove it.

When a chain is active, the sequencer automatically advances to the next slot in the chain at each loop boundary, wrapping around at the end.

7. Transport

BPM and swing update live without stopping playback. Swing delays every second sixteenth note by the set amount, giving a shuffle feel.

The step indicator at the bottom of the transport bar shows the current playback position.

8. Key & Scale

The master key and master scale in the transport bar control all melodic grids by default.

Available Roots

C C# D D# E F F# G G# A A# B

Available Scales

Per-Grid Overrides

Each melodic panel has its own root and scale dropdowns in the panel header. Setting these overrides the master key/scale for that grid only — useful for polytonality or mixing scale colors.

9. Octave Scroll

On melodic grids, click and drag the row labels (the note names on the left edge) up or down to shift the octave range.

• Drag up to move to higher octaves.
• Drag down to move to lower octaves.
• The cursor changes to a north/south resize indicator over the label area.
• Valid range: octaves 0–8.

10. Track Labels

Click a track’s name label to rename it. The label becomes an editable text field.

• Press Enter to confirm the new name.
• Press Escape to cancel and revert.

Custom labels are saved with your project.

11. Drum Row Editing

On drum grids, click a row label (e.g. KICK, SNARE) to edit that row’s name and MIDI note number inline.

• Two small fields appear: the label (left) and the MIDI note number (right).
• Press Enter or click away to confirm.
• Press Escape to cancel.
• Clear both fields to revert to the default GM mapping.

Overridden labels display in the track’s color instead of gray. The override only affects display and MIDI output — saved project files still use the original row names internally, so existing saves load correctly.

12. Volume & Mute

Each track panel has a volume slider and a mute button (M).

• Volume range: −30 dB to +6 dB (default −6 dB).
• Mute: Click M to silence the track. The grid dims to 35% opacity when muted.

Volume and mute state are saved per-track and persist across sessions.

13. MIDI Output

LJam can send MIDI to external instruments and DAWs via the Web MIDI API.

Enabling MIDI

1. Click the MIDI button in the transport bar to enable output.
2. Select one or more MIDI output devices from the dropdown.
3. Your browser may prompt for MIDI permission on first use.

Per-Track MIDI Channel

Each track has a channel selector (1–16). Default channels:

Browser Support

• Supported: Chrome, Edge, Firefox 109+
• Not supported: Safari (desktop & iOS)

MIDI device selections are persisted in localStorage.

14. Patch / Program Change

Each track has a PC / patch text field in the header. This field serves two purposes: sending MIDI Program Change messages and acting as a free-text label for your own reference.

Formats

The field border highlights in the track color when the value is a valid program number or bank+program pair. Every valid patch change sends the full CC#0 (MSB) + CC#32 (LSB) + Program Change sequence, so switching from a banked patch back to a plain number always resets to bank 0,0.

Bank Select LSB (CC#32)

GS devices like the Roland SC-8820 use CC#32 to select between sound maps:

The b:MSB,LSB p:N format lets you address these directly. The short form b:N p:N defaults LSB to 0, which is the native map — identical behavior to plain GM devices where LSB is ignored.

Arrow Key Nudge

Press ↑ / ↓ while the patch field is focused to increment or decrement a value. The cursor position determines which number is affected — place the cursor on the bank MSB, the LSB, or the program number and arrow keys will adjust that part (clamped to 0–127).

When are messages sent?

• On edit — when you press Enter, click away, or use arrow key nudge.
• On file import — all valid patch fields are re-sent after loading a project file.
• On MIDI enable — when you toggle MIDI on, all patch fields are re-sent so your hardware auto-configures.

15. Keyboard Shortcuts

Global

Grid (hover over a grid to activate)

Press a stamp key to enter stamp mode (a colored chip appears in the header). Press the same key again or Escape to exit. On melodic grids, clicking an empty cell places a note of that duration. On drum grids, note length is always 1 step — stamp mode only affects the spacing of drum rolls when dragging. If stamp mode is active when pressing R, notes snap to that duration’s grid.

Velocity levels work the same way: press a number key (1–9, 0=10) to set the velocity for new notes. A “v5”-style chip appears in the header. Press the same key or Escape to clear. Velocity maps to MIDI 25–127 and scales the internal synth volume. Duration and velocity can be active simultaneously. Notes without a velocity level use the track volume as before.

Shortcuts are disabled when a text field, select dropdown, or editable element is focused.

16. Save & Load

Auto-Save

Your project is automatically saved to localStorage after every change (500 ms debounce). It reloads automatically when you reopen the page.

Save to File

Click SAVE in the transport bar to export your project as a .json file. On Chrome and Edge this opens a native file dialog; other browsers download the file directly.

Load from File

Click LOAD to import a previously saved .json file. The file format is versioned and older saves are automatically migrated.

Additional Transport Buttons

• RANDOM ALL — hold to progressively fill all grids (see Randomize below).
• CLEAR ALL — clears every slot across all tracks. Requires a double-click within 2 seconds to confirm.

Randomize (Hold-to-Fill)

Both the per-track randomize button and the RANDOM ALL button use a press-and-hold mechanic:

• Click and release quickly — clears the slot and applies a sparse random pattern. Drums get single-step hits at low density across all rows. Melodic tracks fill only 1–2 rows.
• Hold the button — notes are progressively added every 500 ms. The longer you hold, the denser the pattern becomes.
• Hold with Shift — adds to the existing pattern without clearing first. Useful for layering more notes on top of what you already have.

An undo snapshot is taken when you press down, so Ctrl+Z / ⌘+Z reverts the entire fill in one step.

Per-track randomize and clear buttons affect only the current editing slot for that track.

17. GM Drum Map Reference

When sending MIDI on channel 10, drum tracks use these General MIDI note assignments:

Track 1 — Kick / Snare

Track 2 — Percussion

18. Internal Synth Toggle

The SYNTH ON/OFF button in the transport bar controls whether LJam’s built-in Tone.js synthesizers produce sound.

• SYNTH ON (default) — internal synths play normally.
• SYNTH OFF — internal audio is silenced. The sequencer, step indicator, grid highlighting, and all MIDI output continue running.

Use this when driving external gear or a SoundFont player — you hear only the external sound without the internal synths doubling every note.

Per-track mute buttons still work independently of the synth toggle.

19. MIDI Clock

When MIDI is enabled and the transport is playing, LJam sends MIDI clock messages to all selected output devices:

External apps and hardware can use these messages as a tempo and beat reference. The clock rate adjusts automatically when you change BPM.

20. Using SoundFonts

LJam doesn’t load SoundFont files directly, but you can use an external SoundFont player to get high-quality GM instrument sounds driven by LJam’s sequencer via MIDI.

Setup

1. Install a SoundFont player such as FluidSynth, Qsynth, or sfizz.
2. Load an SF2 file (e.g., FluidR3_GM.sf2) in the player.
3. The player will expose a virtual MIDI input port on your system.
4. In LJam: click MIDI ON, then select the SoundFont player’s port from the output dropdown.
5. Click SYNTH OFF to silence the internal synths.
6. Press play — LJam sends notes via MIDI, the SoundFont player produces the audio.

Selecting Instruments

Use the patch field on each track to send Program Change messages. The SoundFont player will switch to the corresponding GM instrument. For example:

• 0 — Acoustic Grand Piano
• 32 — Acoustic Bass
• 80 — Square Lead
• b:8 p:0 — Bank 8, Program 0 (bank variations)

macOS Quick Start with FluidSynth

1. Install: brew install fluidsynth
2. Run: fluidsynth -a coreaudio -m coremidi /path/to/FluidR3_GM.sf2
3. In LJam, select FluidSynth virtual port as the MIDI output.

21. Factory Reset

If things get into a strange state — unexpected drum mappings, stuck settings, or corrupted project data — you can wipe all saved state and start fresh.

This clears:

• Auto-saved project data (all tracks, slots, chains, patterns)
• Custom drum row labels and MIDI note overrides
• Track labels, patch fields, octave offsets, scale overrides
• BPM, swing, volume, and mute settings
• MIDI output device selections

FACTORY RESET