MIDI implementation

Meiji Sampler’s MIDI surface covers control mapping, a live monitor, and optional transport response.

Control identification

Each MIDI control is uniquely identified by three properties:

Property	Range	Description
Channel	1-16	MIDI channel
Message type	CC or Note	ControlChange or NoteOn
Number	0-127	CC number or note number

A CC on channel 1 number 60 and a Note on channel 1 number 60 are treated as two separate controls.

Mapping behavior

Mappings are one-to-one in both directions:

One control maps to at most one action.
One action maps to at most one control.

When you move a control that already has a mapping, MIDI Learn returns to the Listening list, selects that mapping row, and briefly shows already mapped. Press Enter on the selected row to edit that control’s assignment. When you pick an action that is already mapped to a different control, MIDI Learn also selects the existing mapping row instead of replacing it. Mappings are persisted in the settings file and survive app restarts. After assigning a trigger action, MIDI Learn preselects the next matching trigger target for the next unmapped control:

Last assigned action	Next preselected action
Pad N trigger	Pad N+1 trigger
Loop N trigger	Loop N+1 trigger
Scene N trigger	Scene N+1 trigger
Pad X Chop N trigger	Pad X Chop N+1 trigger

Pad, loop, scene, and chop indices stop at the final display slot, 0. Non-trigger actions keep the exact last assigned action as the next preselected action.

Mappable actions

Transport

Action	Description
Play/Stop	Follow the focused row’s `Space` behavior. Pads stops pad or preview audio first, Loops starts cued or armed transport unless loops are already playing, and Scenes uses the selected scene’s play/cue/stop flow.
Record/Overdub	Toggle recording or punch into overdub on the currently selected loop slot.

Pads

Action	Description
Pad 1-0	Trigger the pad sample and select the channel. If no sample is assigned, the channel is selected but no source-selection modal opens.
Pad N Chop 1-0	Trigger a specific chop slice on the pad. Enters chop mode and plays from the chop marker.

Pad slots use display numbering 1-9 then 0 (matching the keyboard number row).

Loops

Action	Description
Loop 1-0 Trigger	Same behavior as pressing the slot’s number key on the loops row. Empty slots arm, idle stopped slots cue, idle cued slots stop, playing slots queue `STOP+`, and `STOP+` slots stop immediately.
Loop 1-0 Mute	Toggle mute on the loop slot. If any layers are muted, unmutes all first.
Loop 1-0 Solo	Toggle solo on the loop slot. If already soloed, un-solos all.
Loop 1-0 Undo	Undo the most recent loop edit. Note: undo is global, not scoped to the targeted slot. The slot number controls which slot gets UI focus.
Loop 1-0 Clear	Clear all recorded content from the loop slot.

Scenes

Action	Description
Scene 1-0 Trigger	Activate the scene (same behavior as pressing the slot’s number key on the scenes row).
Scene 1-0 Cue	Cue the scene using the `Space`-style scene behavior.
Scene Stop	Stop the currently active scene. If a stop is already queued, executes immediately.

Mixer

Action	Description
Channel 1-0 Mute	Toggle mute on a mixer channel.

Keypress

Action	Description
Keypress	Replay one captured keyboard key through the normal app key handler. Supported keys include printable characters, `Enter`, `Space`, `Tab`, `Backspace`, `Delete`, `Insert`, arrows, `Home`, `End`, `PageUp`, `PageDown`, and function keys `F1` through `F24`. `Esc` is reserved for cancel during capture. Modifier combinations are not supported in this version.

PerformFX

These actions are available when the PerformFX feature is enabled.

Action	Description
Bank A Slot `[1]` through `[9]`, `[0]`	Press and release the fixed PerformFX slot in Bank A. Hold-mode slots stay active while the mapped MIDI control is held.
Bank B Slot `[1]` through `[9]`, `[0]`	Press and release the fixed PerformFX slot in Bank B. Hold-mode slots stay active while the mapped MIDI control is held.
FX Library: preset name	Trigger a named built-in or custom PerformFX Library preset directly. Built-in presets use their recommended defaults. Custom presets use their saved division, Quantize Start, Quantize End, Engage mode, Sync, Attack, Release, One Shot Length, Tail, Throw, PreGain, Wet, and effect-specific parameter settings. Hold-mode presets stay active while the mapped MIDI control is held.
Bank Toggle	Switch between PerformFX banks.
Kill All FX	Kill all active PerformFX effects.

MIDI learn flow phases

The learn flow uses these phases and capture states:

Phase	What happens
Listening	Waiting for a MIDI control movement. Shows existing mappings.
Assigning	Hierarchical menu for choosing an action. Navigate with `Up`/`Down`/`Enter`/`Esc`. Re-trigger the same MIDI control to select the highlighted row without touching the keyboard.
Keypress Capture	Inside Assigning, the Keypress category captures the next supported physical key. `Esc` cancels capture and returns to the category menu.
Editing Behavior	After a CC leaf action is picked for a Gate-eligible target (Loop slot, Channel Mute, Transport, Scene slot, PerformFX slot, PerformFX FX Library preset), choose Trigger or Gate, threshold, and invert. `Enter` saves, `Esc` returns to Assigning. One-shot CC targets (Pad, Cue, Kill All, etc.), Note triggers, and Keypress mappings skip this step and commit directly with the default behavior. Press `B` on any existing mapping in the Listening list to edit its behavior later.

Trigger behavior

Each mapping carries a Behavior that decides how the control’s value drives the action.

Behavior	Fires action
Trigger	Once, on the rising edge above `threshold` (or falling edge if inverted). Default for Pad, PadChop, Scene Cue, Scene Stop, Loop Mute/Solo/Undo/Clear, Record/Overdub, Bank Toggle, Kill All, Keypress.
Gate	Action’s “on” variant on rising edge above `threshold`, “off” variant on falling edge. Default for CC mapped to Loop slot (play/stop), Channel Mute (unmute/mute), Transport (play/stop), Scene slot (start/stop), PerformFX slot (press/release), or PerformFX FX Library preset (press/release).

Both behaviors carry a threshold (1-127, default 64) and an inverted flag (default false).

Note triggers default to Trigger { threshold: 1 }. Note On velocity 0 and Note Off are forwarded as value 0, so stateful actions such as PerformFX Hold slots and mapped FX Library presets receive a falling edge.
CC value 0 is forwarded to the app (it is the falling-edge signal for Gate). Gate mappings will not act on a Recording / Armed loop slot to protect takes in progress.
Mappings loaded from configs saved before this version load with Trigger { threshold: 1 } so existing projects keep their prior behavior.

MIDI tab shortcuts

Mappings sub-view (Listening phase)

Key	Action
`Up` and `Down`	Navigate mapping list
`Enter`	Edit selected mapping
`B`	Edit the selected mapping’s behavior (Trigger/Gate, threshold, invert)
`Delete` or `Backspace`	Remove selected mapping
`Esc`	Leave MIDI tab

Mappings sub-view (Assigning phase)

Key	Action
`Up` and `Down`	Navigate menu
`Enter`	Drill into category or confirm action
Same MIDI control	Drill into the highlighted row or confirm the highlighted leaf action
`Esc`	Go up one menu level, or return to Listening from the top level
`Delete` or `Backspace`	Remove this control’s mapping and return to Listening
`Shift+Delete`	Clear all mappings and return to Listening

Mappings sub-view (Keypress capture)

Key	Action
Supported key	Assign that keypress to the detected MIDI control
`Esc`	Cancel key capture and return to the category menu

Mappings sub-view (Editing Behavior step)

Key	Action
`Up` and `Down`	Move focus between Mode / Threshold / Invert rows
`Left` and `Right`	Adjust the focused field (toggle Gate/Trigger on Mode row; ±1 threshold on Threshold row; flip Invert on Invert row). Hold `Shift` for ±10 on Threshold.
`G` / `T`	Switch directly to Gate / Trigger mode
`I`	Toggle Invert
`Enter`	Save the mapping and return to Listening
`Esc`	Back: return to Assigning (new mapping) or Listening (editing existing)

Key	Action
`Left` and `Right`	Switch between Mappings and Monitor sub-views

MIDI transport

The settings include a transport_enabled toggle. When disabled, transport messages are visible in the monitor but do not trigger transport behavior.

Monitor coverage

The MIDI monitor displays all incoming MIDI events, not just mapping-eligible ones. Visible message types:

Note Off, Note On, Poly Pressure
Control Change, Program Change, Channel Pressure, Pitch Bend
Clock, Start, Stop, Continue
Active Sensing, SysEx, Unknown

Clock and Active Sensing generate high message volume and can flood the display. Use monitor filters to suppress them unless diagnosing a sync problem.

Route allowlist

MIDI mappings use two route rules:

Keypress mappings replay the captured key through the normal key handler after the MIDI control is resolved. They work anywhere the same keyboard key would work, including the Trim/chop editor and other focused modal or view states. The MIDI Mapping assignment page still blocks mapped-controller actions while it is learning a control.
Direct app-action mappings use a conservative allowlist so pad, loop, scene, transport, and mixer actions cannot silently dismiss stateful UI.

The direct-action allowlist is:

Route	Direct-action MIDI allowed	Reason
Pads row	yes	main sampler view
Loops row	yes	main sampler view
Scenes row	yes	main sampler view
Channel Detail	yes	channel overlay — no unsaved state
Channel Chop	yes	chop overlay — no unsaved state
Help overlay	yes	read-only; note that pad actions dismiss Help
All other modals	no	stateful UI could be silently dismissed
All other views	no	stateful UI could be silently dismissed

New modal or view variants added to the codebase are blocked by default. New Channel variants require an explicit allow or block decision at compile time.

If a direct app-action mapping does nothing, check whether the current view is on this allowlist. If a keypress mapping does nothing, verify that the same physical key works in the current UI state. See MIDI And Sync Problems for more.

Current caution

The public marketing copy still describes MIDI controller support as emerging. Use this page as the implementation reference, not as a promise of broader DAW-style MIDI coverage.

MIDI and External Gear — guide to the mapping workflow
Muting And Soloing — explains channel mute versus loop and track mute behavior
MIDI and Sync Problems — troubleshooting
Keyboard Shortcuts — full shortcut reference

Reference

Troubleshooting

Release Notes

MIDI Implementation

MIDI implementation

Control identification

Mapping behavior

Mappable actions

Transport

Pads

Loops

Scenes

Mixer

Keypress

PerformFX

MIDI learn flow phases

Trigger behavior

MIDI tab shortcuts

Mappings sub-view (Listening phase)

Mappings sub-view (Assigning phase)

Mappings sub-view (Keypress capture)

Mappings sub-view (Editing Behavior step)

Sub-tab navigation

MIDI transport

Monitor coverage

Route allowlist

Current caution

​MIDI implementation

​Control identification

​Mapping behavior

​Mappable actions

​Transport

​Pads

​Loops

​Scenes

​Mixer

​Keypress

​PerformFX

​MIDI learn flow phases

​Trigger behavior

​MIDI tab shortcuts

​Mappings sub-view (Listening phase)

​Mappings sub-view (Assigning phase)

​Mappings sub-view (Keypress capture)

​Mappings sub-view (Editing Behavior step)

​Sub-tab navigation

​MIDI transport

​Monitor coverage

​Route allowlist

​Current caution

​Related pages

MIDI implementation

Control identification

Mapping behavior

Mappable actions

Transport

Pads

Loops

Scenes

Mixer

Keypress

PerformFX

MIDI learn flow phases

Trigger behavior

MIDI tab shortcuts

Mappings sub-view (Listening phase)

Mappings sub-view (Assigning phase)

Mappings sub-view (Keypress capture)

Mappings sub-view (Editing Behavior step)

Sub-tab navigation

MIDI transport

Monitor coverage

Route allowlist

Current caution

Related pages