Note: Synchronization Theory: The Basics

We don’t want to overwhelm you with pure theory in this book; our focus is always on practical applications of the concepts in Pro Tools. But in the interest of being clear, here’s just a bit of theoretical perspective, drawn from Vol. 3 (Desktop Audio) of our CSi (Cool School Interactus) CD-ROM series published by Thomson Course Technology, which includes interactive examples that further explain synchronization concepts.

For synchronizing (audio and video) devices, three fundamental time attributes come into play:

• A defined unit of measurement for the information storage method (for example, time units such as hours, minutes, seconds, frames, samples, or inches on a moving tape)

• A nominal rate at which these measurements are taken (how many measurements per unit of time; for example, how many frames, samples or inches per second)

• A stable timing reference that ensures measurements are recorded and reproduced at a precise rate, maintaining their correct time relationship (for example, video sync, sample clock or word sync, capstan tachometer)

In short, we require a measurement, a speed, and a reference that keeps that speed consistent. Lastly, for time-code work, we add a fourth element, timestamp, or location information. Like the address of your house, a timestamp is a precise, numerical reference. It’s used for positioning devices for playback from specific time locations, or to indicate exactly where an event (a video edit, a sound effect, the beginning of a musical cue, and so on) should occur.