Installation manual

UEX/650 Upgrade Kit Installation
6
The AES/EBU Digital Input
With a Cat. No. 794 board installed, the CP650 is capable of handling input
bitstreams from a digital audio source. Possible digital sources include a CD player,
DVD player, satellite television receiver, HDTV receiver, or a HD video player.
Bitstream Format for the Digital Audio Input
The digital input on the Cat. No. 794 can accept a two-channel PCM (pulse code
modulated) bitstream. This is a single bitstream that contains the data for two
channels of PCM audio. It can handle sampling rates of up to 48 kHz with up to 24-
bit resolution. This bitstream format can be found on the digital output connector of a
CD player, DAT recorder, or any basic piece of digital audio equipment.
Interface Standards for Digital Audio
There are two interface types for digital inputs using copper conductors (non-optical
links): AES/EBU and S/PDIF. Even though there are differences in the connectors
used and the interface impedance, the format of the bitstream is generally the same.
One interface can be easily converted to the other if necessary.
AES/EBU STANDARD
The AES/EBU standard has been developed and adopted by professional audio
equipment manufacturers. The standard defines a balanced input (two conductors plus
shield) with a characteristic input impedance of 110 Ω. Equipment incorporating
AES/EBU digital outputs uses conventional-looking XLR connectors carrying digital
bitstreams instead of analog audio signals. Most professional audio equipment utilizes
this format because balanced operation yields superior noise immunity, just like
analog audio. Even in digital audio, noise-free signals are still very important. XLR
connectors have been standard on analog audio equipment, and this is another reason
for their adoption by the professional audio industry. The cable, however, is
specifically designed for digital audio use even though it appears to be the same as
that used for analog signals. Any professional audio equipment or broadcast supply
company can provide 110 Ω cable with connectors (or without, if you wish to
terminate them yourself). Use of cables not designed for 110 Ω digital transmission
will compromise the integrity of the bitstream and may create an unreliable link
between pieces of equipment, particularly with long cable runs.
S/PDIF
The S/PDIF interface, an "unofficial" standard, can be found on consumer
equipment. The interface uses a single-ended input (one center conductor plus shield)
with a characteristic input impedance of 75 Ω and peak-to-peak signal level of
0.5 V. An RCA (phono plug) connector is preferred for consumer equipment such as
CD and DVD players. Although S/PDIF-specific cables with connectors can be
purchased, good results can be obtained using high-quality 75 Ω video cables with the
appropriate connectors and/or adapters.