One of the first things MPE newcomers learn is that every note gets its own MIDI channel, which is what allows per-note pitch bend, pressure and slide. The usual follow-up assumption is that you can therefore play fifteen notes at once. In practice, the real limit depends on several layers: the controller, the host, and the synth's own voice engine. Understanding how they interact explains many of the mysterious "my notes cut off" complaints.
Where the 15 comes from
In the MPE specification maintained by the MIDI Association, a Lower Zone typically uses channel 1 as a "manager" channel for global messages, leaving channels 2 to 16 for notes. That gives 15 member channels. Zones can also be split, with a Lower Zone and an Upper Zone sharing the 16 available channels, in which case each zone has fewer member channels.
Fifteen channels sounds generous, but remember that a note's channel is occupied until its release has finished in the receiving synth, not merely until you lift your finger. A long release tail keeps a channel, and often a voice, busy.
Two different limits
It helps to separate two ideas:
- Channel limit: how many simultaneous notes the controller can address independently.
- Voice limit: how many voices the synthesizer can actually render, which depends on its polyphony setting and CPU load.
A synth set to 8 voices will start dropping notes after eight, even if your controller could send fifteen. Conversely, a controller configured for only a few member channels will reuse channels sooner, which can cause one note's expression to bleed into another.
What note stealing does
When a new note arrives and no voice or channel is free, something has to give. This is voice allocation, and the common strategies are intuitive. Stealing the oldest note is the most natural for sustained sounds; stealing the lowest or highest note can suit bass or lead playing; and some systems offer a never steal mode that simply ignores the new note instead.
The free MPE Emulator plugin is a good place to see these options laid out, because it exposes allocation strategies such as never steal and steal lowest, highest, oldest or newest. Even if you never use it, its parameter list is a handy checklist of the decisions every MPE chain makes somewhere.
Spotting the symptoms
Allocation problems tend to show up in recognisable ways:
- Notes cut off during dense chords or fast runs. Likely a voice limit, so raise polyphony or shorten release times.
- Expression "jumping" between notes. A channel was reused before the previous note finished releasing. Increase the number of member channels or reduce release length.
- The same chord sounds different each time. Allocation order is affecting which voices are stolen. Choose a deterministic strategy.
- Stuck or hanging notes. A note-off was lost or misrouted, often at a zone boundary or when switching presets mid-performance.
Practical settings
Start by checking your controller. Many MPE devices let you choose the number of member channels. Using all fifteen reduces channel reuse, while a smaller number can be useful if your synth only responds to a limited range. Hardware such as the LinnStrument and Expressive E's Osmose offer MPE configuration options, so consult their manuals for the exact settings.
Next, look at the synth. Make sure its polyphony is high enough for your playing style, and match its MPE zone configuration to your controller. Mismatches here are among the most common causes of strange behaviour.
Finally, check the host. Hosts such as Bitwig Studio and REAPER handle MPE in their own ways, and it is worth confirming how each routes channels to plugins before blaming the instrument.
The takeaway
MPE gives you fifteen channels of independent expression, but it does not give you unlimited polyphony. Think of channels, voices and release times as a shared budget. Tune them together, pick an allocation strategy that suits the music, and your notes will end when you want them to, not when the engine runs out of room.