Background

What is synchronization?

Synchronization is the process of getting 2 or more devices to play back together at the same speed and position. These devices can range from audio and video tape machines to digital audio workstations, MIDI sequencers, synchronization controllers, and digital video devices.

Synchronization basics

There are 3 basic components of audio/visual synchronization: position, speed, and phase. If these parameters are known for a particular device (the master), then a second device (the slave) can have its speed and position “resolved” to the first in order to have the 2 devices play in perfect sync with one another.

Position

The position of a device is represented by either samples (audio word clock), video frames (timecode), or musical bars and beats (MIDI clock).

Speed

The speed of a device is measured either by the frame rate of the timecode, the sample rate (audio word clock) or by the tempo of the MIDI clock (bars and beats).

Phase

Phase is the alignment of the position and speed components to each other. In other words, each pulse of the speed component should be aligned with each measurement of the position for the most accuracy. Each frame of timecode should be perfectly lined up with the correct sample of audio. Put simply, phase is the very precise position of a synchronized device relative to the master (sample accuracy).

Machine control

When 2 or more devices are synchronized, the question remains: how do we control the entire system? We need to be able to locate to any position, play, record, and even jog and scrub the entire system using one set of controls.

Machine control is an integral part of any synchronization setup. In many cases, the device simply called “the master” will control the whole system. However, the term “master” can also refer to the device that is generating the position and speed references. Care must be taken to differentiate between the 2.

Master and slave

Calling one device the “master” and another the “slave” can lead to a great deal of confusion. The timecode relationship and the machine control relationship must be differentiated in this regard.

In this document, the following terms are used:

• The “timecode master” is the device generating position information or timecode.

• The “timecode slave” is any device receiving the timecode and synchronizing or “locking” to it.

• The “machine control master” is the device that issues transport commands to the system.

• The “machine control slave” is the device receiving those commands and responding to them.

For example, Nuendo could be the machine control master, sending transport commands to an external device which in turn sends timecode and audio clock information back to Nuendo. In that case, Nuendo would also be the timecode slave at the same time. So calling Nuendo simply the master is misleading.