By ttessarolo
Tue Aug 04, 2026 3:16 pm
Sharing a fix that took me a while to find, because I couldn't find it documented anywhere.
Setup: MPC One G2 (MPC 3.9, standalone) using a Behringer XR18 as its class-compliant audio
interface over USB. XR18 set to 44.1 kHz (mandatory — the MPC won't go above 44.1 with
class-compliant interfaces).
Symptom: right after boot everything is clean, in both directions (recording into the MPC
from the mixer, MPC playback through the mixer). But as soon as I loaded a real project
(~5 tracks), playback started crackling — and it would NOT recover on its own. The only way
to get clean audio back was a full power-cycle of everything... until the next project load.
Cable was direct (no hub), "32 Inputs/Outputs" unchecked, and there is no audio buffer
setting on the MPC side, so there was nothing left to tweak.
THE FIX (found by accident):
Preferences -> MIDI -> Output Ports -> uncheck SYNC on "XR18 MIDI 1".
That's it. Instantly stable, even with heavier projects.
Why it works (my best understanding): with Sync enabled, the MPC sends MIDI Clock + transport
out of that port — 24 messages per quarter note, each one timing-critical. But "XR18 MIDI 1"
is the MIDI port of the SAME USB composite device that carries the 18x18 audio streams, so
clock and audio were competing on the same cable, serviced by the same host. The MPC drives
class-compliant audio with a fixed 128-sample buffer (no adjustment possible) and its USB
audio stream doesn't re-sync after an underrun. On an empty project there's enough headroom
for both; under project load the two hard-real-time streams collide, the audio stream slips,
and it stays broken until USB re-enumeration (i.e. the power cycle).
Notes:
- You lose nothing that matters: MIDI Program Changes to the XR18 (snapshot recall) still
work. The Sync checkbox only controls clock/transport, not track MIDI.
- If you need MIDI Clock for external gear, send it from the physical DIN MIDI OUT instead.
Rule of thumb: never send MIDI Clock over the same USB connection that carries your audio,
at least on a fixed-buffer class-compliant host like the MPC.
- I'd expect the same to apply to the X32 and any other interface with a built-in USB MIDI port.
Hope it saves someone else the headache.
Setup: MPC One G2 (MPC 3.9, standalone) using a Behringer XR18 as its class-compliant audio
interface over USB. XR18 set to 44.1 kHz (mandatory — the MPC won't go above 44.1 with
class-compliant interfaces).
Symptom: right after boot everything is clean, in both directions (recording into the MPC
from the mixer, MPC playback through the mixer). But as soon as I loaded a real project
(~5 tracks), playback started crackling — and it would NOT recover on its own. The only way
to get clean audio back was a full power-cycle of everything... until the next project load.
Cable was direct (no hub), "32 Inputs/Outputs" unchecked, and there is no audio buffer
setting on the MPC side, so there was nothing left to tweak.
THE FIX (found by accident):
Preferences -> MIDI -> Output Ports -> uncheck SYNC on "XR18 MIDI 1".
That's it. Instantly stable, even with heavier projects.
Why it works (my best understanding): with Sync enabled, the MPC sends MIDI Clock + transport
out of that port — 24 messages per quarter note, each one timing-critical. But "XR18 MIDI 1"
is the MIDI port of the SAME USB composite device that carries the 18x18 audio streams, so
clock and audio were competing on the same cable, serviced by the same host. The MPC drives
class-compliant audio with a fixed 128-sample buffer (no adjustment possible) and its USB
audio stream doesn't re-sync after an underrun. On an empty project there's enough headroom
for both; under project load the two hard-real-time streams collide, the audio stream slips,
and it stays broken until USB re-enumeration (i.e. the power cycle).
Notes:
- You lose nothing that matters: MIDI Program Changes to the XR18 (snapshot recall) still
work. The Sync checkbox only controls clock/transport, not track MIDI.
- If you need MIDI Clock for external gear, send it from the physical DIN MIDI OUT instead.
Rule of thumb: never send MIDI Clock over the same USB connection that carries your audio,
at least on a fixed-buffer class-compliant host like the MPC.
- I'd expect the same to apply to the X32 and any other interface with a built-in USB MIDI port.
Hope it saves someone else the headache.