PCI-822 User’s Guide
19
Using the PCI-822
This chapter provides some basic set-up information to help you
connect the PCI-822 card to many popular digital tape machines,
mixers, and external converters.
In addition to using the proper cables with the correct connectors, it’s
important to have exactly one audio clock master and to have all other
digital devices follow that master.
Synchronization
Every digital audio system operates at a particular sample rate,
such as 44,100 samples per second (44.1kHz) for audio CDs. The
sample rate can be explicitly transmitted between devices (through a
TDIF cable or by BNC word clock) or it can be embedded in a digital
audio stream that uses a self-clocking format (SPDIF or AES/EBU).
The sample rate can also be derived from NTSC or PAL video signals.
When two or more digital audio devices transfer data, one and only
one of them should be used to set the sample rate. This device can
have a variety of names — system clock source, sync source, sample
clock master, audio clock master, or word clock source. The master
device uses an internal oscillator to set the sample rate. All other
devices must be synchronized (slaved) to the sample clock master, so
their digital clocks are locked to the master clock.
No two oscillators run at exactly the same rate, even if they’re both
44.1kHz oscillators (for example). Therefore, if two devices in a
system are set to internal sync, each using its own internal oscillator,
one is inevitably a bit faster than the other. As a result, samples are
lost or duplicated during the transfer, corrupting the audio.
