pi-Stomp Manual Using

MIDI Implementation

Default CC map

Control CC Type Value range
Footswitch A 60 Toggle 0 (off) / 127 (on)
Footswitch B 61 Toggle 0 (off) / 127 (on)
Footswitch C 62 Toggle 0 (off) / 127 (on)
Footswitch D 63 Toggle or tap tempo 0 (off) / 127 (on)
Tweak 1 70 Continuous 0–127
Tweak 2 71 Continuous 0–127
Volume (Tweak 3) — Audio card Hardware volume
Expression pedal 75 Continuous 0–127

MIDI routing

pi-Stomp controls → ALSA Midi Through (client 14:0)
  → JACK (-X seq)
    → mod-host:midi_in (MIDI Learn for parameter control)
    → MOD-UI (for wiring to LV2 MIDI plugins)

MIDI learn

Any plugin parameter can be mapped to any MIDI CC:

  1. In MOD-UI, open the plugin's settings dialog
  2. Click the parameter modify button (next to the parameter you want to assign)
  3. Select MIDI, then Save
  4. Move the control (footswitch, knob, expression pedal, external controller)

The parameter is now mapped. Save the pedalboard to retain the assignment.

MIDI mode must be set to Separated (not Aggregated) for MIDI learn to work correctly.

Un-assigning a control

A control cannot be assigned to a new parameter until it is un-assigned from the old one. Open the modify dialog for the parameter it's currently bound to, click None, then Save.

Assigning only a certain range

The assignment dialog has an Advanced button exposing Range (min–max). The custom range doesn't clip the parameter — it replaces the port's declared range in the transform, so all 128 MIDI steps redistribute across the shorter span:

value = min + (max − min) × (cc / 127)

Narrow a 0–10 drive to 5–10 and full counter-clockwise on the tweak knob now lands at 5, with each step worth 0.039 instead of 0.079. You spend the whole controller on the half of the range you actually use, at double the resolution.

Two things to know. The parameter can no longer reach its own floor from the hardware — only from MOD-UI. And on a port marked logarithmic the curve is computed against your custom range rather than the port's, value = min × (max/min)^(cc/127), which mod-host carries a FIXME for; a custom minimum of 0 on such a port makes that ratio undefined.

External MIDI

With the MIDI + Expression Add-On Kit, the 1/8" TRS jack provides MIDI in/out. External controllers connected via USB are also supported.

To route a pi-Stomp control to an external MIDI device instead of the internal virtual port, configure midi_port: in the pedalboard's config.yml. See the Configuration page.

Tap tempo

Footswitch D sends tap tempo BPM via WebSocket (transport-bpm), not MIDI. The tempo is applied to plugins that support host tempo (e.g., Bollie Delay with Tempo Mode set to MOD/Host).

Clock source

Tap tempo sets the tempo only when the pi-Stomp is its own clock. The clock source is a three-way choice — Internal, Ableton Link, or MIDI Clock Slave — set in the Audio & MIDI menu.

Set it to match who's in charge of time. If the pi-Stomp is following a drummer's track or a DAW, put it in Link or MIDI Clock Slave and stop worrying about tapping. If it's leading, leave it Internal.

Whichever source is active, tempo-synced plugins follow it the same way — via host tempo — so the choice doesn't change how you set a delay up, only where its clock originates.

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