H.1. Running status

23.0403GPPRelease 17Technical realization of the Short Message Service (SMS)TS

In the Musical Instrument Digital Interface (MIDI) standard, a key-on or a key-off event will use at most three bytes each, cf. [40], However, in case several key events occur on the same MIDI-channel, running status can be used. In principle running status means that the first byte of, e.g. key-on is omitted. In addition, the key-on event having a velocity of zero is equivalent to the key-off event. Thus, combining running status and using key-on with zero velocity, as the key-off event will reduce the number of bytes needed to encode key events.

EXAMPLE: Without running status, the sequence

91 2E 23 8E, 91 2B 50 8E, 81 2E 64 00, 81 2B 64 00

means “Key 2E ON” Velocity 23 MIDI Ch 1”, “Key 2B ON Velocity 50 MIDI Ch 1”, “Key 2E OFF Velocity 64 MIDI Ch 1”, “Key 2B OFF Velocity 64 MIDI Ch 1”. Using running status will reduce the sequence into

91 2E 23 8E, 2B 50 8E, 2E 00 00, 2B 00 00,

That is, the command byte is omitted and velocity zero is used for key off.