You can use Audio Synchronization settings to keep your audio and MIDI tracks synchronized.
When Show Advanced Tools is selected in Advanced preferences, the following are available:
MTC slider: Shows the deviation between the incoming MTC and its nominal frame rate. If the deviation is significant, make sure that the correct frame rate is set in the General Synchronization pane. If in doubt, set the frame rate to 24 fps and select “Auto detect format of MTC” in the General pane. If the frame rate is correct, you can use this display to adjust the tape speed of the master machine to the nominal value (the same speed used when the timecode was recorded). Adjust the varipitch control on the master machine, until the slider is centered.
Sample Rate slider: Shows the deviation of the sample rate from its nominal value. Note that some audio hardware doesn’t allow any variation in the sample rate.
Deviation slider: Shows the current phase deviation of the Word Clock from the timecode master—in other words, the deviation between audio and MIDI. Varying timecode signals shown in this display indicate how Logic Pro regulates the sample rate of the hardware when in MTC Continuous sync mode. Even large timecode variations result in no deviation between audio and MIDI synchronization. Your audio hardware must be capable of continuously variable sample rates for this to function. Small deviations between audio and MIDI are unavoidable, because MIDI can (and should) follow the timecode master directly.
Note: The real-time sample rate conversion feature of Logic Pro allows it to follow an external MTC signal (MTC Continuous), while maintaining the correct audio playback pitch and speed. This feature works even when recording in MTC-slave mode.
When Additional Audio Options is selected in Advanced preferences, the following is available:
Core Audio pop-up menu: Defines how your Core Audio hardware is synchronized to an external timecode master.
MTC Continuous: Audio regions are started in sync, and the sample rate is continuously regulated to match variations in the timecode master signal. Even very long audio regions stay in sync in this mode.
MTC Trigger + Auto Speed Detection: Similar to MTC Trigger (see below), but the tempo of the timecode master is constantly monitored while Logic Pro is running. The next time you start Logic Pro, it uses an adapted sample rate. This mode keeps long regions in better sync with the timecode master, although not as closely as MTC Continuous. It does, however, use a constant sample rate, which isn’t affected by variations in the timecode master signal.
MTC Trigger: Audio regions are started in sync, but are then played at a constant sample rate, regardless of any variations in the timecode master signal. Logic Pro always uses the set nominal sample rate (44.1, 48, 88.2, 96, 192 kHz). This mode is suitable when it is vital to retain the absolute pitch of a recording. If the speed of the timecode master deviates from the nominal value, you may need to split long audio regions into shorter sections.
External or Free: Logic Pro has no influence on the sample rate. The audio hardware is responsible for ensuring that the position and sample rate of audio regions match. This mode is advisable only if you’re sure the Word Clock and timecode master are running in sync—by using an external SMPTE or Word Clock synchronizer, for example.