User manual

494
Synchronization
Background
What is synchronization?
Synchronization is the process of getting two or more de-
vices to play back together at the same exact speed and
position. These devices can range from audio and video
tape machines to digital audio workstations, MIDI sequenc-
ers, synchronization controllers, and digital video devices.
Synchronization basics
There are three basic components of audio/visual synchro-
nization: position, speed, and phase. If these parameters
are known for a particular device (the master), then a sec
-
ond device (the slave) can have its speed and position “re-
solved” to the first in order to have the two 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 compo-
nents to each other. In other words, each pulse of the
speed component should be aligned with each measure
-
ment of the position for the most accuracy. Each frame of
timecode should be perfectly lined up with the correct sam
-
ple of audio. Put simply, phase is the very precise position
of a synchronized device relative to the master (sample ac-
curacy).
Machine control
When two 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 mas-
ter” 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 dif-
ferentiate between the two.
Master and slave
Calling one device the “master” and another the “slave”
can lead to a great deal of confusion. The timecode rela-
tionship and the machine control relationship must be dif-
ferentiated in this regard.
In this document, the following terms are used:
• The “timecode master” is the device generating position infor-
mation 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 trans-
port commands to the system.
• The “machine control slave” is the device receiving those
commands and responding to them.
For example, Cubase could be the machine control mas-
ter, sending transport commands to an external device
which in turn sends timecode and audio clock information
back to Cubase. In that case, Cubase would also be the
timecode slave at the same time. So calling Cubase sim
-
ply the master is misleading.
Ö In most scenarios, the machine control slave is also
the timecode master. Once it receives a play command,
that device starts generating timecode for all the timecode
slaves to synchronize to.
Timecode (positional references)
The position of any device is most often described using
timecode. Timecode represents time using hours, min
-
utes, seconds, and frames to provide a location for each
device. Each frame represents a visual film or video frame.
Timecode can be communicated in several ways:
• LTC (Longitudinal Timecode) is an analog signal that can be
recorded on tape. It should be used for positional information
primarily. It can also be used for speed and phase information
as a last resort if no other clock source is available.