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Dolby® Encoding and Monitoring
Channel Mode
The Channel Mode control (7-1A) sets the configuration of the audio output channels embedded in the AC-4
bitstream. Choices include 2-channel (stereo), 5.1-channel, or 5.1.4-channel outputs (5.1-channel "base layer"
with ear-level channels + 4 overhead channels).
Frame Rate
The Dolby AC-4-encoded audio frames be aligned with video frames to prevent losing audio frames or introducing
A/V sync errors during source switching, much like Dolby E or ED2. The frame rate control (7-1B) should be
set to match the video frame rate in your particular workflow. Select "Native" when there is no video reference
available.
Bit Rate
The Dolby AC-4 codec provides increased efficiency compared with Dolby AC-3 (Dolby Digital) to allow for the
delivery of Dolby Atmos and multi-language content. The optimal bitrate for any given application – set by the Bit
Rate control (7-1C) - will depend on a number of variables including channel mode and additional dialogue and
music and effects content in NGA applications, but the basic recommendations are listed below.
Channel
Configuration
Stereo (2/0)
5.1
5.1.4
Type
AC-4 can deliver a traditional single mix, consisting of dialogue, music, and effects elements. This is referred to as
a "complete mix" and often abbreviated as "CM".
It can also deliver a single common music and effects element ("M&E") together with separate dialogue elements
("D") with each dialogue element selected and mixed with the M&E element in the AC-4 decoder. This ability is
what allows for "personalized audio" as different elements can be combined into multiple audio presentations and
delivered within a single bitstream.
Local emergency audio can also be delivered in the bitstream.
The Type control (7-1G) identifies whether the stream is Complete Main, Music and Effects, or Dialog. Cur-
rently, only Complete Main is supported.
Note:
Emergency Audio is signaled by selecting EAS audio as the Priority 1 source when configuring input groups.
Please see Chapter 5 for more information.
Recommended
Dolby AC-4 Data Rate
64 kbps
144 kbps
288 kbps
Chapter 7 | 31
Equivalent
Dolby AC-3 Data Rate
192 kbps
382 kbps
N/A
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