Installation guide

TDM Installation Guide20
Internal This is the 888/24 I/O standard setting.
In this mode, the 888/24 I/O sample rate is gen-
erated by its internal crystal oscillator (whose
frequency is determined by the Sample Rate set-
ting in the Session Setup window). Internal
mode should be active whenever the 888/24 I/O
is not synchronized to an external clock source.
Digital This setting indicates that an AES/EBU or
S/PDIF word clock signal is currently the source
for the 888/24 I/O sample rate. This is the set-
ting to use for inputting material from DAT re-
corders or other digital devices.
To use the 888/24 I/O digital inputs and outputs
as effects sends and returns to digital effects de-
vices, you should set the 888/24 I/O to Internal
mode. You should then set the digital effects de-
vice to accept an external digital clock (from the
888/24 I/O) so it synchronizes itself to
Pro Tools.
The 888/24 I/O can only synchronize to and re-
ceive word clock lock on channels 1–2 of its dig-
ital inputs. To synchronize your system to an
external digital clock source, it must be con-
nected to digital inputs 1–2 of the 888/24 I/O.
In an expanded Pro Tools system, the system
clock is carried by the audio interface connected
to the first Pro Tools card in your system. This
audio interface will act as the master interface in
your system. All other audio interfaces will be
slaved to it.
Slave This LED is lit when the 888/24 I/O sam-
ple rate is synchronized to another Digidesign
audio interface or synchronization peripheral.
In this mode, the sample rate of the slave inter-
face is derived from the frequency of the incom-
ing master clock signal present at the Slave
Clock In (256x) port.
The 888/24 I/O automatically switches to this
mode when a Slave Clock Out signal from an-
other Digidesign interface, Universal Slave
Driver, Video Slave Driver, or SMPTE Slave
Driver is connected to the 888/24 I/O Slave
Clock In port.
In expanded Pro Tools systems, the Super Clock
output of the master audio interface locks all
other interfaces together with sample accuracy,
keeping all signals phase-synchronous.
Sample Rate and 1–2 Format Indicators
These LEDs indicate the sample rate of the
888/24 I/O internal crystal oscillator and the
digital format (AES/EBU or S/PDIF) of the audio
input signal to channels 1 and 2.
The choice of digital format for these two chan-
nels is made in the Session Setup window or
Hardware Setup dialog. Digital input pairs 3–4,
5–6, and 7–8 of the 888/24 I/O are always
AES/EBU. Sample Rate is set in the Session Setup
window or Hardware Setup dialog in Pro Tools.
The 888/24 I/O provides the following sample
rates:
Because some digital audio devices do not
output proper clock when they are not play-
ing back, leaving the 888/24 I/O in Digital
mode may cause Pro Tools audio playback
quality to suffer, or play back at the wrong
pitch. If you are using digital I/O, reset the
Sync Mode from Digital to Internal after in-
putting material.
When slaving to a Digidesign Universal
Slave Driver, Video Slave Driver, or SMPTE
Slave Driver, set the clock source to Internal.
The audio interface will automatically
switch to Slave mode when it detects the
256x input clock
TDM_Install.book Page 20 Saturday, January 13, 2001 9:35 PM