When you first open Logic Pro X, it is in Internal Sync (master) mode. The control bar Sync button, if visible, is not activated.
When Logic Pro X is running as a synchronized slave, the control bar Sync button is activated.
You can use the Sync button to turn external synchronization on or off at any time, without changing the selected synchronization source. This allows you to temporarily disengage Logic Pro X (running as a slave) from an external synchronization master device and could prove useful, for example, if you need to quickly edit a MIDI region while the external synchronization source—tape machine, VTR, and so on—is still running.
You can use the Sync button shortcut menu to choose a synchronization source.
Note: The control bar Sync button is not displayed by default.
Control-click the control bar, then choose Customize Control Bar from the shortcut menu.
Select the Sync checkbox toward the bottom of the Modes and Functions column, then click OK.
Click the control bar Sync button to synchronize Logic Pro to the chosen synchronization source.
Control-click the control bar Sync button to open a shortcut menu, then do one of the following:
Set the type of external synchronization (a synchronization source). Choose from:
Internal Sync
SMPTE Sync (MTC)
Manual Sync (Tempo Interpreter)
Auto Sync In
Determine if MMC commands should or should not be transmitted when using the Logic Pro X control bar buttons. MMC commands are used for remote control of MIDI-controlled tape machines. See MIDI Machine Control.
Open the Synchronization settings. See General Synchronization settings.
Open the tempo editors. See Tempo overview.
Click the upper (MIDI In) section of the MIDI Activity display while receiving an external synchronization signal.