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 up to 26 slots and 8 chains for building arrangements on the fly, and plays to one output: the built-in synth, a sample kit, or a MIDI device.

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–Z)

Each track has up to 26 independent slots labeled A through Z. Think of them as pattern variations for a single track. Slot tabs appear as you need them: every slot in use is shown, plus one empty tab after the last, so a fresh track shows two tabs and a busy one shows what it uses. A slot that holds notes, sits in a chain or is painted in the arranger is never hidden.

• 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. Arranger

The arranger is a timeline strip under the transport bar for building a song out of your slots and chains. Each row is one track, each column is one bar. Click ▸ ARRANGE to unfold it.

Painting blocks

• Each row has a brush shown next to the track name. It is the slot currently selected for editing in that track's panel. Click the brush to switch it to that panel's editing chain instead.
• Tap an empty bar to paint a block of the current LEN (1, 2, 4 or 8 bars).
• Drag sideways to paint a block as long as the drag.
• Drag down across several rows to paint every row with its own brush at that bar.
• Tap an existing block to remove it. Painting over a block replaces it.
• A slot loops inside its block for the block's length.
• A chain brush unrolls the chain as you paint: chain A B painted over six bars gives A B A B A B, each member taking its natural length (1 bar, or 2 if it has notes in bar 2). Every stroke starts the chain from its first member. The result is ordinary slot blocks, so you can erase or repaint any one of them.
• Blocks are references to slots: editing slot B changes every B block. Editing a chain does not change blocks already painted from it.

Playing a song

• Switch the mode button from JAM to SONG. In Song mode the arrangement decides which slot each track plays, and a track with no block at the current bar is silent.
• Click the bar ruler to set the start bar. Press play to run from there.
• Drag on the bar ruler to set a loop range and turn LOOP on. The LOOP button toggles it without losing the range.
• With the loop off, playback stops at the end of the last block.
• You can still jam on top of a song: queued slots and mutes work as usual until the next block starts.
• In Jam mode the arranger is ignored and everything behaves as before.

The arrangement is saved with the project. CLR removes every block and is undoable.

8. 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.

VU next to it opens a small output meter: the fill is the RMS level, the bar the peak, the white tick the held peak and the dot lights on a clip (ticks at −24, −12, −6 and 0 dBFS). Click it again for an oscilloscope of the output, and once more to hide it. While the meter is on, a thin level line runs under every track’s VOL slider. A full-velocity hit on any track peaks around −12 dBFS with its fader at 0 dB, so six tracks at the default −6 dB stay under 0; faders at +6 will clip the master, which has no limiter.

9. 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.

10. 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.

11. 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.

12. Drum Row Editing

Row level

On drum grids, drag a row label (e.g. KICK, SNARE) up or down to trim that row’s level, from −24 to +6 dB. The thin bar under the label shows where it sits, and the label reads the value while you drag. Alt-click resets it to 0 dB. The trim applies the same way whatever the track’s OUT is: it scales the built-in synth, the sampler, and MIDI velocity. Per-hit accents are still the note velocities; this is the static mix of the row. A sample that is simply recorded too hot is better trimmed once in Waverly, where the gain travels with the kit.

Name and MIDI note

Double-click a row label 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.

13. Volume, Pan & Mute

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

• Volume range: −30 dB to +6 dB (default −6 dB).
• Pan: L100 to R100, centre by default; double-click the slider to centre it. It pans the built-in synth and the sampler alike and is saved with the jam. MIDI tracks are panned on the receiving instrument.
• 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.

14. Track Output: Synth, Sampler, MIDI

Every track plays to exactly one output, chosen from the OUT menu in its header. Nothing is global: there is no master synth or MIDI switch, and a track never plays to two places at once.

Want a kit and a hardware synth on the same part? Use two tracks with the same pattern (alt-click a slot tab to copy it).

Kits are built and edited in Waverly, the sample editor served beside LJam: the WAVERLY link in the transport bar and “Edit kits in Waverly…” at the bottom of the OUT menu open it in its own tab. Both apps share one browser sample library, so a kit tagged there appears in the OUT menu here when you come back to this tab.

MIDI

1. Your browser asks for MIDI permission when LJam loads. The MIDI device select then appears in the transport bar.
2. Tick the default outputs there, as many as you like: an IAC bus into a SoundFont player and the hardware interface at the same time, for instance. The set is remembered per browser, not per project, because it describes how this machine is wired.
3. Set a track’s OUT to MIDI, or press ALL MIDI to route every track. ALL SYNTH brings them all back.
4. If one instrument should get only its own output (say the PMA-5 on DIN 1), pin that track with its Port field. Every other track follows the default set, so changing the set re-steers them all at once.
5. Set the channel. Default channels when you first switch a track to MIDI:

A device that is unplugged shows as (missing) in red; a track whose outputs are all missing plays silence until one returns or you pick another. The light next to the outputs select is green while some track is sending to a connected device. Pinned ports are saved with the project by id and name; the default set is not.

Browser Support

• Supported: Chrome, Edge, Firefox 109+
• Not supported: Safari (desktop & iOS) — the MIDI section of the OUT menu is simply absent.

15. Patch / Program Change

A track routed to MIDI has a PC / patch text field next to its channel selector. It sends a MIDI Program Change (with optional Bank Select) whenever you change it, when the track is switched to MIDI, when the project loads, and when the device reconnects.

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.

16. 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.

17. 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.

18. 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

19. MIDI Clock

While the transport is playing, LJam sends MIDI clock messages to every device that any track is routed to:

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: tick the SoundFont player’s port in the transport bar’s MIDI outputs, then set tracks to MIDI (or press ALL MIDI). Tracks left on SYNTH keep playing internally.
5. 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, tick FluidSynth virtual port in the MIDI outputs.

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