Click the attached mp3, "Polyphony and Expressive Polyphony" to download an audio example. You'll hear a single chord played twice.
The first chord is played on one MIDI channel with 3-note polyphony. This is an example of an ordinary MIDI instrument. Control messages like pitch bend (Glide), aftertouch (Press) and CCs (like Slide) affect all three notes equally. The timbre of the notes changes together.
The second chord is played on multiple channels. This is an example of the Seaboard's multi-dimensional expression. This is 3-note expressive polyphony. You can hear that the control messages are applied to each note individually. The timbre of each note can modulate and morph entirely separately of the others.
Polyphony
Polyphony refers to the number of notes that an instrument can perform simultaneously. For example, when playing a synth with 1-voice polyphony (called monophonic), you can hear one note at a time, and attempting to perform a second note simultaneously will cancel out the first.
Now click the attached mp3, "Monophonic example," to download a different audio example.
In this example, the notes are all played on one MIDI channel. Some MIDI control messages – like pitch bend – are "channel-wide" so they apply to all notes equally. For example, when playing a chord on a standard MIDI keyboard the pitch wheel will pull all notes in the chord up or down by equal amounts.
Expressive polyphony
When we set a channel range for the Seaboard or Lightpad Block, we determine not only polyphony, but expressive polyphony.
The important difference in expressive polyphony is that each note's data is sent on its own MIDI channel, which allows for polyphonic expression of those control messages which would otherwise apply to all notes.
For example, with expressive polyphony you may bend the pitch and timbre of individual notes without affecting the pitch or timbre of the other notes being played at the same time.