Controls note-stealing behavior for a single pitch, when using note_polyphony. Allowed values are on and off, default is on.
Default self-masking behavior is that higher-velocity notes turn off lower-velocity notes, but lower-velocity notes do not turn off higher-velocity notes. This is generally desirable when playing repeated piano notes, ride cymbals, hammered dulcimers etc. With note_selfmask set to off, notes turn off notes with the same pitch regardless of velocity, which generally sounds less “musical” but does ensure that note polyphony is always preserved within the set limit, and can sound right for certain instruments.