MIDI Sync Messages (RTM)

MIDI RTM messages are used to synchronize the tempo between Grid and other devices. This allows sequencers, drum machines, DAWs, and other MIDI equipment to stay perfectly in time with each other.

The examples below show how to enable MIDI Clock message handling and how to receive clock messages in a callback.

Enable Clock Messages

Sync messages are disabled by default. You can enable them using the RX Mode block. Add the block to the System Element Setup and enable MIDI RTM.

Receiving Clock Messages

When a MIDI Clock message is received, the callback below is executed.

-- Callback for received clock messages
self.rtmrx_cb = function(self, header, rtm_byte)
  print("RTM RX: "..rtm_byte)
end

Understanding the Callback

The rtm_byte value contains the received MIDI real-time message.

Common MIDI Sync messages:

Message	Decimal Value	Description
Clock	248	Sent 24 times per quarter note to keep devices in sync
Start	250	Starts playback from the beginning
Continue	251	Continues playback from the current position
Stop	252	Stops playback

Example

If a DAW sends MIDI Clock while playing, the callback will continuously receive:

RTM RX: 248
RTM RX: 248
RTM RX: 248
...

When playback starts:

RTM RX: 250

When playback stops:

RTM RX: 252

This allows your script to react to transport controls and tempo synchronization events.