Metric Halo 2882 operating guide - Manual (Page 24)

Mobile I/O User’s Guide
16
There are four different ways to get external clock information into the unit:
1. Sending a 1x word clock signal into the WC Input BNC.
2. Sending a 256x word clock signal into the WC Input BNC.
3. Sending an AES or S/PDIF signal into the Digital input.
4. Sending an ADAT optical signal into the Optical input.
The BNC word clock input port is a 75 Ohm terminated coaxial input. It
should be driven by a 75 Ohm source driver and interconnected with 75
Ohm coaxial cable. If you do not use proper cabling and source drive, you
will introduce reflections on the word clock cable which will propagate jit-
ter into the recovered word clock. This is true whether you use the port as a
1x WC input or a 256x WC input, but becomes more important when the
clock signal is 256x.
1x is generally appropriate for use with devices that provide a word clock
output. If your device provides a 256x output, you may find that you get bet-
ter results using that clock signal. The Digidesign® line of Pro Tools® prod-
ucts use 256x as their “Superclock™” clocking signal.
The AES recommended procedure for distributing clock is to use an AES
clock signal. The AES clock signal is an AES digital audio signal with no
audio activity. Mobile I/O only uses the AES preambles for clock recovery, so
it is immune to data dependent jitter effects. This means you can reliably use
the Digital Input as a clock source with or without audio data.
Finally, you can recover clock from the optical input sent to the Mobile I/O
from another ADAT device. In general, if you want to use the ADAT optical
input to receive audio, you will want to choose the ADAT optical input as
the clock source.
F IRE W IRE
FireWire® is Apple’s registered trademark for the IEEE 1394 High-Speed
Serial Bus. FireWire started as an Apple technology to replace a variety of
interface ports on the back of the computer. After promulgating a number of
closed proprietary technologies in the early days of the Macintosh, Apple
determined that open standards were better for the Mac, for the industry,