Metric Halo Mobile I/O - Manual (Page 64)

2882 Users Guide
64
The Optical SPDIF communication protocol allows a device to transmit 2 channels of 24 bit audio at 96kHz,
along with digital audio clock information.
Since Mobile I/O provides direct routing within the box, you can easily configure the unit to work as an ADAT
based 8 channel A/D/A. Refer to the chapter on MIO Console for information about configuring the routing.
Clock Sync
Clock sync is a serious consideration in any digital audio system.
If you are recording analog sources with 2882, you can simply use the unit’s high-quality internal clock source
to drive the converters. This is the easiest case to deal with.
If you need to interface with other devices digitally or ensure sample accurate sync with video sources, the
extensive clock synchronization capabilities of 2882 will prove to be more reliable (and better sounding) than
most higher priced alternatives.
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 signal into the Optical Digital 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 jitter 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 better results using that clock signal. The Digidesign® line of Pro
Tools® products 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. 2882 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.
FireWire
Detailed information on FireWire implementation can be found in the FireWire appendix.
Power
One of 2882’s great strengths is the flexibility of its power system. 2882 can be powered from any DC source
(including bus power) in the range of 9V to 30V as long as it provides 12 Watts of power. The DC input on
the 2882 is a 2.1mm coaxial power connector, center positive. So if you are powering the unit with a third
party power source and it supplies 9V, the power source will have to provide 1.4 amps of current. If you are
powering the unit with 12V, the power source will have to provide 1 amp of current, and so on.
The 2882 ships with a world-ready 24 volt, 2 amp power supply. You can plug this supply into any AC power
source from 90V to 240V, 50Hz - 60Hz, using an appropriate IEC power cord, and it will supply the proper
power to the 2882 on the 2.1mm coaxial power connector. 2882 will automatically supply the extra power to
the FireWire bus. This means that the 2882 and its power supply can be used to power other bus-powerable
FireWire devices including hard-drives, hubs, and other 2882 units.
Since 2882 is DC powered, you can also power up the 2882 using the FireWire bus or another DC source.
The 2882 uses 12 Watts of power, so the device supplying the bus power must be capable of sourcing that