Dolby Digital) Notes; Output Mode; Multiplexer Timing Issues - Linear Acoustic LA-5448 User Manual

Linear Acoustic LA-5448 AC-3 Frame Synchronizer/Rate Shaper User Guide
3.1 AC-3 (Dolby Digital) Notes
The maximum data rate that is supported by the LA-5448 is 448 kbps. Rates higher
than this will be displayed as an error condition. When stream shaping is turned on,
no changes are made to AC-3 content. All metadata and audio parameters are passed
exactly as originally encoded with the exception that the data rate will now be fixed
at 448 kbps.
Several additional parameters and configurations are described below.
3.1.1

Output Mode

Typical external AC-3 encoders (i.e. Dolby DP569) or other AC-3 sources may have
several selections for output mode, which simply determines where inside an AES
pair the relatively tiny AC-3 data packets are carried. It does not matter which selec-
tion is chosen as long as the LA-5448 and the encoder match. The default for the LA-
5448 is Pro-32, the default for most known professional equipment that generates or
passes AC-3. The result of mis-setting this is that the output audio will mute.
3.1.2

Multiplexer Timing Issues

Tandberg encoders supply an AES reference signal that may be in the form of a fifth
wire with a BNC connector attached (later models), or it may be an XLR connector,
possibly of the opposite sex (i.e. an XLR Female) requiring an AES balun. There also
may be a menu setting to enable this reference output (automatically enabled in later
models). This reference MUST be used to drive the local AC-3 encoder's reference
input. It is NOT necessarily the same as plant reference as it is derived from the en-
coder's internal 27MHz clock. Save some headaches and lost sleep, and use this pro-
vided connection!
NOTE: Tandberg encoders provide an external reference output which MUST be
used to lock the local AC-3 encoder.
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Applications