MIDI Polyphonic Expression – or MPE – is a method of using MIDI which enables multidimensional devices like the Seaboard 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.
In conventional MIDI, channel-wide messages (such as pitch bend) are applied to all notes being played on a single channel. In MPE, each note is assigned its own channel so that those messages can be applied to each note individually.
How is it implemented?
When a device is transmitting MIDI according to MPE, it will use a range of channels:
The lowest 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 remaining channels (usually Channels 2–16) are used to transmit notes and expressive data on a note-per-channel basis – this data will only apply to the note which is on the same channel.
ROLI Dashboard allows you to select the note channels and automatically uses the channel immediately below that range for the Global channel. For example, if the channel range were changed to 5–16, then ROLI Dashboard would automatically select Channel 4 as the Global 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.