Matters Concerning Audio - A Practical Guide to Video and Audio Compression - page 151

One of the major benefits is that it electrically decouples the source and destination
equipment. This means that problems such as ground loops, hum, mains-induced inter-
ference, and other nasty things that happen to electrical signals when they pass through
magnetic induction fields are completely eliminated. Any potential difference in voltage
between the two chassis is also isolated. These are all good things when putting together
an audio installation. It is useful on location recordings when you are jacking a feed across
from the house PA or the stage's main mixing console.
The Apple G5 computer now has SPDIF built into the motherboard and while there
were some issues with “chirping” noise artifacts being propagated through from the
power supply in a few of the 2003 early-vintage models, this has been eliminated in the
updated products. A replacement power supply resolves the issue if you buy a second-
hand machine that exhibits the problem.
If you are having trouble identifying an SPDIF connector on an unlabeled rack, con-
sult Appendix M where a collection of audio and video connectors have been collated
together for reference.

7.3.5 Digital Audio via USB

For some applications, taking digital audio in via a USB interface may be a satisfactory
solution. As a general rule though, this interface is not as fast as FireWire although it is
more popular on PC platforms. MIDI interfaces are often provided as a USB connection,
and bear in mind that keyboard and mouse traffic also share this interface.
Instinctively I feel more secure putting multi-channel, high sample-rate audio down
a FireWire interface but if USB is all you have and your audio transfer needs are modest,
it should be fine, at least for a couple of channels at a 44.1 or 48 KHz sample rate.
If you plan to do your audio via USB, then an M-Audio interface would be a good
choice. It has been engineered to deliver the optimum performance. A range of models are
available to suit different requirements.

Figure 7-4 Omni studio USB I/O unit. Source: Image courtesy of M-Audio.