A Word About Digital Clocks - Alesis adat AI4 Reference Manual

2
Signal Connections

A Word About Digital Clocks

In chapter four, we'll illustrate some applications for your AI4. But first, a
brief explanation of digital clocks is in order. It's critical that every unit
being connected with a digital connector like an ADAT Optical cable is
running at the same clock speed.
Digital audio signals like the ADAT Optical format are made up of
digital sample words. Each word is a burst of numbers: a 24-bit, 48kHz
signal is made up of a word 24 bits long, played 48,000 times every
second. If the sending unit and the receiving unit aren't in perfect sync,
the signal will be distorted. For example, if an ADAT was running at
48,000 samples per second (48kHz), and your digital mixer was running
at 48,001 samples per second, you would hear a "click" when the samples
didn't exactly line up.
The way to fix this is to set every unit in your studio to run from the
same master clock. Whether it's an ADAT, computer-based editing
workstation, digital mixer or DAT machine, you need to designate one
unit in your studio as the master clock.
Every other digitally-connected unit needs to slave to this master. When
routing signal between digital devices, the AI4 allows you to decide
which device will be the master clock. Because you can change the clock
source with a simple push of a button, you can decide which devices are
masters and slaves as the situation warrants. Remember, though, that you
also need configure to clock source of each device to the appropriate
setting. The master device should be set to its internal clock; all other
devices are slaves, and should be configured to sync to external clock.
Once you've cabled everything in, it's time to power up your gear. You
can turn on your gear in any order, but note that whichever unit you've
designated as clock source master must be turned on for the units
designated as slaves to functions properly.
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