Reference Guide

1091
SMPTE/MIDI time code synchronization
Synchronizing your gear
SMPTE/MTC sync and full chase lock
When using SMPTE/MTC Sync with full chase lock, the first time you play any audio the pitch may
fluctuate wildly for up to 30 seconds. Also, you may occasionally note the pitch of the audio sounding
consistently high or low pitch.
A simple analogy makes this behavior easy to understand: Synchronizing audio to SMPTE/MTC is a
lot like trying to get even and stay neck-and-neck with another car on the freeway. If the car is ahead
of you, you need to drive faster to catch up to it. If it's behind you, you have to slow until the car
catches up to you. Once the two cars are neck-and-neck, you can simply keep going at the same
speed, unless the other car changes its speed. If the other car speeds or slows, you must speed or
slow too.
The first time you play audio under SMPTE/MTC Sync, the audio clock has to get even with the
external clock. This could mean racing ahead, which raises the pitch of the audio, or stepping on the
brakes, which lowers the pitch of the audio. These fluctuations continue until SONAR matches its
playback speed to the external clock, which usually takes no more than 30 seconds. The stable
playback speed, by the way, may be slightly faster or slower than the normal audio playback speed,
resulting in a slight change in the pitch of the audio. Here’s the best way to address this problem:
• Start each new SONAR session by playing some audio under SMPTE/MTC Sync.
• Let the audio play for 30 seconds or until all audio pitch fluctuations stop.
Once this procedure is complete, SONAR knows the difference in rates between the external time
code and the audio clock on your sound card. For the rest of the session, SONAR will start playback
closely in sync, without any drastic pitch changes.
If the external timing source were 100 percent stable, the audio would stay in sync with the external
clock. Unfortunately, no timing source is perfect. Therefore, every once in a while after playback has
started, SONAR may need to vary the playback speed by a tiny amount to stay even with the time
code. If the time code signal is unstable (as might be the case from an analog source), these
variations can cause noticeable changes in audio pitch, which can in turn cause audible audio
distortion.