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6.33. DOLBY AC3 ENCODER CONTROL TAB
The 7812 series module can encode Dolby AC3E with the Dolby AC3E options installed. There can be
more than one Dolby AC3E module installed. The controls for each Dolby AC3E encoder are identical.
Since each Dolby AC3E Encoder Control tab is identical, only Dolby Decoder B will be described.
UNDERSTANDING THE DOLBY AC-3 ENCODER
The on-card Dolby AC-3 encoder takes the output of Mixer-B and a selected source of metadata to
encode a single AC-3 encoded output. This output can be substituted to any output pair (including
duplicating to any number of outputs) and routed to the AES and embedded outputs.
There is neither a frame-rate relationship nor a frame phase relationship between the AC-3 packet and
the video frame. Either switches of encoded AC-3 outputs, discrete AES or embedded, into the video
signal will result in packet corruption issues.
There are certain restrictions to what can be encoded to AC-3 relating to the LFE (low frequency effects)
channel, bit-rate and audio configuration. LFE (low frequency effects channel), can only be included on
audio configurations of 3/2, 2/2, 3/1, 2/1 and 3/0.
There is also a restriction on the minimum bit-rate allowed for specific audio configurations. The following
table indicates what bit-rates are allowed (shaded boxes indicate the bit-rate is not allowed):
7812UDXD Series 3G/HD Up/Down/Cross Converter with Simultaneous Dual Format Outputs and AES I/O
Figure 6-38: Dolby AC3 Encoder Control Tab
kbps
3/2
3/1
224
Y
Y
256
Y
Y
320
Y
Y
384
Y
Y
448
Y
Y
512
Y
Y
576
Y
Y
640
Y
Y
Table 6-1: Encoder Bit-rate Restrictions
Revision 1.1.1
7800/7700 MultiFrame Manual
2/1
2/0
1/0
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
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