Table of Contents
Advertisement
When one device sends out a bit of data (like the ball being thrown to the
other juggler), the other needs to be ready to receive it. If the data is being
sent even just slightly faster than it can be received, bits will be lost,
causing errors in the audio (like the ball being dropped).
Similarly, if the data is being sent even slightly slower than the receiver
expects it to be, then the receiver will occasionally be left without real data
at its input (like a juggler grabbing at the air). In digital audio, these errors
show up as loud pops and clicks, as well as lower-level noise.
The rate at which those bits are sent and received is controlled by the word
clock, which "ticks" for every bit of data. Each device has its own word
clock, so that it can work on its own–such as a single ADAT, or a single
1212 I/O.
When you send digital audio data between two devices, however, their
word clocks need to be synchronized together, so that devices send and
receive each bit at the exact same moment. One of the devices–usually the
sender–will provide the master clock; the other will ignore its internal
clock, and instead slave to the master clock.
This clock signal is normally carried along with the digital audio data, so
that when connecting two devices together in a simple configuration–such
as dubbing between two DAT machines–you don't need to make any other
connections. Sometimes, however, it is necessary to send the word clock
separately from the digital audio data–as in the case of the BRC, for
example.
As part of the BRC's master control functions, it provides the word clock
for the connected ADAT system; since the BRC does not actually send or
receive audio data, it sends the word clock through the ADAT sync cables.
To control the BRC's word clock–necessary when transferring audio from
S/PDIF to ADAT, for example–you must use a separate word clock
connection to synchronize the BRC to the S/PDIF source.
Editing ADAT audio off-line
As explained above, a digital audio device's word clock controls the speed
of the digital audio bit-stream, and unless the clocks of two devices are
explicitly synchronized, they will tend to run at slightly different speeds.
This means that the same DAT tape, played in two different, un-
synchronized DAT machines, will play slightly slower in one of the
machines–and thus will play for a slightly longer time. The difference will
be so slight that you almost certainly couldn't hear it in isolation, but if you
made an exact copy of the tape and played the two tapes back at the same
time on un-synchronized machines, you'd notice that they would drift
apart over time.
The same thing can happen when transferring audio data from an ADAT
system to the 1212 I/O. As long as ADAT is select as Clock Source for the
Korg 1212 I/O
System Configurations
21
Advertisement
Table of Contents
