Dolby CP750 Digital Cinema Processor Manual - Projectionniste.net

Chapter 2
Installation
2.1 CP750 Floating Signal Grounds
The CP750 is designed to eliminate ground loops, which can occur when the unit is
connected to multiple external equipment grounds. For this reason, the following CP750
connectors have isolated grounds:
• MAIN AUDIO OUTPUT and MULTI-CHANNEL ANALOG INPUT—Eight‐channel input and
output are balanced and floating. Note that a common mode signal between the
CP750 audio outputs and its chassis ground must not exceed +6 V peak.
• AUTOMATION connector—The common is floating and can be +5 V peak from the
chassis ground.
• 1xAES IN BNC digital inputs—These are transformer isolated and their grounds can
be +10 V peak from the chassis ground.
• 4xAES D‐connector digital inputs—These are transformer isolated and their grounds
can be +10 V peak from the chassis ground.
Note:
The RS‐232 input ground is connected to the CP750 chassis ground and is not
floating.
2.2 Digital Audio Inputs
There are two professional interface standards for digital audio transmission: AES/EBU
(also known as AES3) and AES‐3id. These methods stream the same digital data and
professional audio header information over copper conductor links, but use different types
of conductors and connectors.
AES/EBU uses a balanced connection (two conductors plus shield) with a characteristic
input impedance of 110, a nominal peak‐to‐peak signal level of 5 V, and, most commonly,
XLR connectors. The typical maximum transmission distance is 100 meters (328 feet).
AES‐3id uses an unbalanced connection (one signal conductor plus shield) with a
characteristic input impedance of 75, peak‐to‐peak signal level of 1 V, and BNC (“push
and twist”) connectors. The typical maximum transmission distance is 1,000 meters (3,280
feet).
Professional digital audio equipment typically uses the AES/EBU method because
balanced operation yields superior noise immunity, as it does with analog audio signals,
and because XLR connectors are the standard on analog professional audio equipment.
Professional video equipment typically uses the AES‐3id interface, with BNC connectors.
As with XLR connectors on professional audio equipment, the adoption of BNC
connectors for the audio on professional video equipment stems from their use for the
video signal. Also, the unbalanced AES‐3id signal can connect to more than one piece of
Dolby ® CP750 Digital Cinema Processor Manual 11