MPE (MIDI Polyphonic Expression)
An extension to MIDI that gives every single note its own pitch bend, pressure and timbre control by putting each note on a channel of its own.
Classic MIDI sends pitch bend and aftertouch per channel, and one channel usually carries a whole instrument. Bend one finger in a chord and the entire chord bends. MPE fixes this with a convention rather than a new protocol: a zone of up to 15 channels, each new note assigned its own, so that bend, pressure and the third dimension (CC 74, usually wired to the filter) apply to that note alone.
The demand came from instruments like the Roli Seaboard, Roger Linn's LinnStrument and the Haken Continuum, where fingers slide and press on a surface rather than just striking a key. The MIDI Manufacturers Association adopted the spec in 2018. Since it is just ordinary MIDI with discipline, it runs over 35-year-old cable — provided the synth at the other end knows what's going on.