Jack Transport (Linux only) adds the ability to sync Renoise with multiple Jack clients on Linux. This allows audio programs to be in sync with each other, all connected via Jack Transport. You can start, stop and relocate the play position from any of the Jack enabled applications. All software "jacked into" the session will react and synchronise accordingly.
Levels of Jack Transport Control
Level 1: Each Jack client has the power to start, stop and relocate (change the playback position of) the transport. This is represented in either seconds or sample time.
Level 2: Only one Jack client can control the Time Base, which is the tempo, time signature and beat position.
Most applications support the first level of Jack Transport control. The second level is, at the time of writing, rarely supported. If there is more than one application running which supports the Time Base, Jack will select one automatically.
Dealing with Tempo
Tempo information is exchanged only when the synchronized application supports Time Base. As stated above, most applications do not support this and so you will have to set the tempo manually.
In the case where all Jack Transport applications are Time Base aware, you still have to make sure that all clients are using the same tempo and automation. This is because playback relocation will be done in sample time instead of "beat time". All clients need to have the same base tempo in order to jump to the same positions.
Dealing with Loops
There is no loop information in the Time Base. Every client will try to apply its own loops, fighting with the other Jack programs to reposition. To avoid this conflict, enable loops in the application that is currently active and disable them in the others.
PDC and Jack Transport
Jack doesn't provide a way to explicitly handle latencies. When PDC (automatic plugin delay compensation) is enabled in Renoise and, for example, you want to use Ardour to tell Renoise to jump to pos 0, Renoise will attempt to compensate by jumping to "Pos 0 + overall PDC Latency". This offset may result in a small misfire. If this becomes a problem you should temporarily disable PDC in Renoise.
Configuring Jack Transport
The option to turn on Jack is in the Audio Preferences panel. Jack Transport is disabled by default, even when Jack is selected as the audio device in Renoise.