MIDI System Real-Time Messages

MIDI System Real-Time Messages
Message Description
F8 - Timing Clock MIDI clock.
This message is used to sychronise timing across sequencers in a MIDI system. (note 1)

24 clocks = 1 quarter note

F9 - Undefined The current Running Status is not affected.
FA - Start Used to synchronise the start-up of sequencers
The sequence must start from song position 0

Sequencing begins at song-position 0 when the next Timing Clock message is received (note 2)
(note 3)

FB - Continue Continue
Used to tell a sequencer to continue playing the current song from where it last left off.

The sequencer should continue from the current song-position when the next Timing Clock message is received (note 2)
(note 3)

FC - Stop Used to tell a sequencer to stop playing.
Any subsequent MIDI Timing Clock messages are to be ignored.

Note-off messages should be sent for all notes which are still on, and all controllers should be returned to their 'normal' settings.

The current song position pointer should be stored, so that playing can continue from the same point if a MIDI Continue message is received.
(note 3)

FD - Undefined The current Running Status is not affected.
FE - Active Sensing This signal may be sent by a MIDI transmitter when there is no other activity. (note 4)

It is sent after every 300ms (nominally) of inactivity.

A MIDI transmitter should send this message after 270ms of inactivity, while a MIDI receiver should expect it within 330ms.

Once this message is received, Active Sensing is 'on', and the receiver should perform an All-Notes-Off if there is no MIDI activity for more than 330ms.

It is functionally similar to a 'carrier' signal for a modem - it indicates the 'line' is still operational.

FF - System Reset System Reset.
The system should be set to the following states:
  • Omni on, Polyphonic
  • Local control on
  • All notes turned off
  • All controllers returned to their 'normal' settings
  • Any song playing stopped
  • Song Position Pointer = 0
  • Running Status is cleared
  • Reset to power-up conditions


Note 1
A MIDI Real Time message, in particular the MIDI Timing Clock message, may be inserted into the middle of another message, without affecting that message or cancelling the current Running Status.
Note 2
The requirement to wait for the next MIDI Timing Clock only applies if the sequencer is being synchronised from an external MIDI clock, rather than its own internal clock.
Note 3
Any superfluous Real Time messages should be ignored. For example, if a Start message is followed by a subsequent Start message, the second Start message should have no effect.
Note 4
There is no requirement for a MIDI device to support Active Sensing either as a transmitter or a receiver. It must be ignored by a receiver if it is not supported.


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