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.