Dolby Laboratories DP570 - Manual (Page 100)

88 Dolby ® DP570 Multichannel Audio Tool User’s Manual
A Guide to Dolby Metadata Dynamic Range Control
D.3 Dynamic Range Control
Different home listening environments present a wide range of requirements for dynamic
range. Rather than simply compressing the audio program at the transmission source to
work well in the poorest listening environments, Dolby Digital encoders calculate and send
Dynamic Range Control (DRC) metadata with the signal. This metadata can then be
applied to the signal by the decoder to reduce the signal’s dynamic range.
Through the proper setting of DRC profiles during the mastering process, the content
producer can provide the best possible presentation of program content in virtually any
listening environment, regardless of the quality of the equipment, number of channels, or
ambient noise level in the consumer’s home.
Many Dolby Digital decoders offer the consumer the option of defeating the Dynamic
Range Control metadata, but some do not. Decoders with six discrete channel outputs (full
5.1‐channel capability) typically offer this option. Decoders with stereo, mono, or
RF‐remodulated outputs, such as those found on DVD players and set‐top boxes, often do
not. In these cases, the decoder automatically applies the most appropriate DRC metadata
for the decoder’s operating mode.
The Dolby Digital stream carries metadata for the two possible operating modes in the
decoder. The operating modes are known as Line mode and RF mode due to the type of
output they are typically associated with. Line mode is typically used on decoders with six‐
or two‐channel line‐level outputs and RF mode is used on decoders that have an
RF‐remodulated output. Full‐featured decoders allow the consumer to select whether to
use DRC and if so, which operating mode to use. The consumer sees options such as Off,
Light Compression, and Heavy Compression instead of None, Line mode, and RF mode.
Advanced decoders may also allow custom scaling of the DRC metadata.
All that needs to be done during metadata authoring, or encoding, is selection of the
dynamic range control profiles for Line mode and RF mode. The profiles are described in
the following sections.
Line Mode
Line mode offers these features:
• Low‐level signal boost compression scaling is allowed.
• High‐level signal cut compression scaling is allowed when not downmixing.
• The normalized dialogue level is reproduced from the decoder at a constant loudness
level of –31 dBFS Leq(A), assuming the Dialogue Level parameter is set correctly.
Line‐level or power‐amplified outputs from two‐channel set‐top decoders, two‐channel
digital televisions, 5.1‐channel digital televisions, Dolby Digital A/V surround decoders,
and outboard Dolby Digital adapters use Line mode.
Consumer control of the dynamic range is limited when downmixing. Products with stereo
or mono outputs do not usually allow consumer scaling of Line mode. This is because these
Note: While the use of DRC modes during decoding is a consumer‐selectable feature, the
Dialogue Level parameter setting is not. Therefore, setting the Dialogue Level
parameter properly is essential before previewing a DRC profile.