MIDI Clock is a MIDI protocol that allows the syncing of playback (transport and tempo) of multiple sequencers, synthesizers, drum machines etc. This can be external MIDI hardware, other software on your computer, or software running on other computers and connected to Renoise via MIDI cables.
There are two MIDI Clock modes: master and slave. Renoise fully supports both modes.
The MIDI Clock master sends a series of 24 ppqn (pulses per quarter note) beat clock messages to all slaves. The interval of these messages allows the connected slaves to determine the master's tempo and beat position. Along with the 'beat clock' messages, 'Start', 'Stop', 'Continue' and 'Relocation' (Song Position Pointer) messages are sent to sync the timelines of the master and slaves.
Only the MIDI Clock master can start or stop the playback or change the tempo. Slaves are forced to follow the master, thus the terms 'master' and 'slave'.
Running Renoise as MIDI Clock Master
Set Up Devices
To use Renoise as the master, simply set up a MIDI Clock master device in the "Edit -> Preferences -> MIDI" panel. You can also specify which message types should be sent from Renoise. Send only MIDI Clock messages if you just want to transfer tempo to the slaves. Note that Renoise only sends out MIDI clock messages while playing back a song.
You can use the "Offset" slider in the "MIDI Clock Master" preferences to shift clock messages back and forth in time. This is sometimes needed to compensate delays (phase offsets) that are introduced by MIDI hardware. The easiest way to test and adjust this is by using a steady metronome sound on both the master and slave. If the sounds do not play back on exactly the same beat, try adjusting the "Offset" slider in Renoise until they match.
Please note that the smallest possible negative latency is limited to the current latency of your soundcard. If you need further negative latency, you can increase your audio latency in the Audio Preferences.
Running Renoise as MIDI Clock Slave
Set Up Devices
To connect Renoise to a MIDI Clock master, use the MIDI Clock slave device section in the "Edit -> Preferences -> MIDI" panel.
To quickly enable and disable the connection to the master clock, use the small 'Clock' button in the Renoise Transport Panel, next to the BPM. This icon will only show up when a MIDI Clock slave device has been set.
Important: A MIDI device must be selected and the sync clock mode icon must be enabled to sync Renoise to other devices. After you have done this, you should notice a small green blinking LED at the top of the Renoise interface:
The LEDs next to the small clock icon show the MIDI Clock input in green and output in red.
As with the MIDI Clock master mode, you can correct small offsets between Renoise and the master with the "Offset" slider in the preferences. Again, the easiest way to test and adjust the offset is by using a steady metronome on both the master and slave. If the sounds are not in sync, try adjusting the offset slider in Renoise until they match.
MIDI messages often only have very rough timing, so the beat clock messages transferred from a MIDI Clock master to Renoise may be imperfect. Depending on how precise the incoming MIDI clock stream is, you can use this option to set how fast Renoise should react to changes from the MIDI Clock master. The higher the Smoothing value, the more stable the sync will be, but the slower Renoise will react to 'real' BPM changes from the master. Try playing around with the Smoothing to find a good value for your setup.
Loading New Songs Without Losing Sync
You can detach and reattach Renoise to a running master at any time without losing sync. To do so, simply stop the song in Renoise when running as MIDI Clock slave, instead of stopping the master. Now you can even load a new song and hit start again, whereupon Renoise will resync itself as smoothly as possible to the master, which is still playing. This is extremely useful when playing live, because you can continuously run a master and also switch songs in Renoise. When reattaching Renoise in this manner, the closer you start playing to an on-beat, the less correction will be needed and the smoother the adjustment will be.