MIDI Polyphonic Expression – or MPE – is a method of using MIDI which enables multidimensional devices like the Seaboard and BLOCKS to control multiple parameters of every note within MPE-compatible software. ROLI instruments, including the Seaboard RISE, Seaboard GRAND, and BLOCKS, as well as other instruments like the Continuum, Soundplane, and Linnstrument, use MPE to let musicmakers control pitch, timbre, and other nuances within each note.
ROLI instruments use MPE to transmit their dimensions of touch as standard MIDI messages on multiple channels to achieve expressive polyphony.
- Each note is sent on an individual channel
- Messages which would normally influence all notes (like pitch bend or continuous controllers) can be expressed polyphonically.
In conventional MIDI, pitch bend and CCs (Continuous Controllers) are channel-wide messages, meaning that they apply to all notes being performed on that channel. An ordinary MIDI controller sends all notes on the same channel so the pitch bend or CCs are applied to all of those notes equally. For example, if you hold a chord on a normal MIDI keyboard and then move the pitch wheel, all the notes will bend together.
In MPE, each note is assigned its own channel so that these messages can be applied to each note individually. By using a separate channel for each note, MPE instruments are able to transmit these controllers individually for each note – without influencing the other notes being performed.
This means that when recording the MPE data, your DAW must be able to receive and record multiple channels. If the pitch bend or CC data for several notes is summed into one channel, they will clash and the sound will be erratic.
How is it implemented?
When a device is transmitting MIDI according to MPE, it will use a range of channels:
One channel (usually Channel 1) is used for global messages – data such as preset changes and pedal positions are transmitted on this channel to apply to all notes equally. The global channel is set by the "MPE Zone." When the MPE Zone is the Lower Zone, Channel 1 is used for global messages. When the MPE Zone is Upper Zone is, Channel 16 is used for global messages.
The remaining channels (usually Channels 2–16) are used to transmit notes and expressive data – including note-on velocity, pitch bend, channel pressure (aftertouch), CC74 (brightness), and note-off (release) velocity – on a note-per-channel basis. The expressive data will only apply to the note which is on the same channel.
How does it work with Equator?
When Equator receives MIDI according to MPE, it listens to Channel 1 only for global messages like the sustain pedal or the Seaboard RISE's Touch Faders and XY Touchpad, and Equator listens to Channels 2–16 for notes and their accompanying expressive data.
How does it work with other software?
Can I download the MPE specification?
Yes – the approved MPE spec is attached below.