Connection
Connect the SP-404 MkII via USB-C, then Setup > "Connect to SP-404".
On desktop use Chrome or Edge; on iPhone/iPad use the MIDIWeb Browser app.
FX control works in MIDI mode A and B; patterns need mode B + "PC Rx" ON.
If the app seems outdated, load the URL with ?v=99 (cache); the build number is shown in Setup.
Status bar and tabs
Connection dot (tap = Setup), TX blinker, BPM on incoming clock,
Overview/Focus, XY, ALL OFF (all buses off + remembered; a second tap restores),
Snap, Setup. Tabs: BUS 1–4, IN, PLAY, PTN – the LEDs show active effects.
Fader gestures (Focus)
Relative drag – the first touch never jumps. Fine-tune: while dragging,
pull sideways (finer from 60 px, very fine from 120 px). Double tap = default.
Tap the value window = ±1 stepper. Desktop: mouse wheel ±1, Shift ±10.
EFX pad: tap = on/off, hold = momentary.
‹/› step through favorites. RND randomizes (sparing LEVEL/SEND/GAIN),
then acts as UNDO for 6 s.
Effects
Tap the effect name to open the picker: Recent, Favorites (star via hold),
categories. The bus types have different sets (Roland's spec) –
Sync Delay & co. only on BUS 3/4, voice effects only on INPUT.
Direct FX: mirror in Setup what sits on the device's DFX 1–5 –
the faders then show real parameter names. The app remembers values per effect
and sends everything to the device on each switch.
Snapshots (Snap)
8 slots for all 5 buses. Tap loads (empty: saves),
hold saves with inline naming, ✕ deletes. Export/import as JSON –
also for moving snapshots between devices.
XY pad and LFOs
Assign both axes at the top; position = value. MOMENTARY springs back on release.
Four LFO slots (chips 1–4): target, wave (SIN/TRI/SQR/SAW/RND = drift),
rate in note values, depth. Time source: CLK (MIDI clock) or TAP
(tap the beat). A finger on the target fader pauses and re-centers;
switching off parks at the center.
PLAY
KEYS: keyboard – sample chromatic (CH 16, C2–C4) or
vocoder (CH 11) with pitch-bend strip. SCALE: 4×4 grid with only
in-scale notes; ISO = Move layout (rows a fourth apart), LIN = continuous;
roots highlighted. PADS: pad board laid out like the device
(pad 1 top left), banks A–J, ★ = custom layout (hold to assign);
PAD-CH must match the device setting "Pad MIDI Channels".
PTN: patterns, autopilot, looper
Pick a bank, tap a pattern (mode B + PC Rx ON; highlighted = last sent).
The autopilot wanders quantized every 2/4/8 bars, optionally within the bank.
The looper panel remote-controls the device's looper mode (REC, OVERDUB, DEL,
UNDO/REDO, STOP ALL, BPM).
Tempo / Ableton Link
BPM reads MIDI clock from any port (AUM, Ableton, a bridge). Link route:
the Link source sends clock to the SP-404 (UTILITY > SYSTEM > MIDI: "MIDI Sync")
and to this computer – everything runs in sync. LFOs/autopilot use the clock, else tap tempo.
Keyboard (desktop)
1–5 = bus · Space = EFX · O = overview · X = XY · Esc = close.
Tips and limits
No SysEx: the app cannot see effect changes made on the device (encoders do arrive) –
switch effects from the app. BUS 3/4 silent? Device-side bypass: toggle the EFX pad
off/on once (the app does this automatically on effect switches). The app never sends
on load – align via "Send state to device" or the first gesture.
About
404 Busdriver is an unofficial open-source project (MIT license) and is not
affiliated with or endorsed by Roland Corporation. "SP-404" is a trademark of
Roland Corporation. Effect data derived from the public SP-404MK2 reference manual.