Dolby Laboratories DP570 Specifications download pdf (Page 10)

Standards and Practices for Authoring Dolby

Digital and Dolby E Bitstreams

Dialogue Normalization in a Dolby Digital decoder cannot be defeated. Dialogue

Normalization alone does not assert any compression or expansion on the program

material but simply adjusts the audio to a standardized level (See ATSC A52

www.atsc.org/Standards/stan_rps.html).

That being said, Dialogue Normalization works in partnership with two other

optionally assertable (or defeatable) parameters within the Dolby Digital bitstream,

collectively called the Dynamic Range Control Profiles. The Dialogue Normalization

parameter determines the area within the program audio where the Dynamic Range

Profiles are inactive, setting a null band between the soft and loud portions of the

program where no audio processing occurs and defining the upper and lower limits of

the Dynamic Range Profiles.

Again, while the Dialogue Normalization parameter is required and not defeatable,

the Dynamic Range Profiles are optional and can be turned off in a properly

implemented Dolby Digital decoder. This means the choice to listen to a program at a

reduced dynamic range (so as not to disturb the neighbors), or to the same program in

all its full-volume, earth-shaking glory, is entirely up to the consumer.

3.5 Dynamic Range Control

Dynamic Range Control (also known as Dynamic Range Compression) within the

Dolby Digital data stream consists of two profiles: Line Mode and RF Mode. These

two profiles do not change the content of the encoded audio within the bitstream, but

are used by the Dolby Digital decoder to adjust the extremes of the program material

within the listening environment to account for those instances where it is preferable

or necessary to listen to the program at a reduced dynamic range.

Line mode provides a moderate amount of compression when compared with RF

mode, and also allows the user to adjust the low-level boost and high-level cut

parameters within a home decoder when not downmixing. This adjustment or scaling

of the boost and cut areas allows the consumer to customize the audio reproduction

for their specific listening environment. To avoid clipping, the scaling feature is not

available in certain downmixing situations. RF mode is designed for peak-limiting

situations where the decoded program is intended for delivery through an RF input on

a television, such as through the antenna output of a set-top box. The RF Mode

Profile is also used for a common feature on consumer decoders known as “Midnight

Mode,” which provides enough dynamic range compression to ensure that an action

movie or game won’t wake up others in the home.

In contrast to compression as used on musical instruments in a recording studio to

make them sound punchy and fat, dynamic range compression limits the softest and

the loudest portions of an audio program to maintain a comfortable and intelligible

listening level. For example, when enjoying a movie (on DVD, video, or broadcast

TV) at lower volumes, the softer portions of the program (whispers, softer dialogue,

etc.) are more difficult to hear, requiring greater volume, thereby making the louder

portions (explosions, onscreen arguments, gunshots, etc.) too loud for comfortable

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Dolby Laboratories DP570 Specifications Page 10

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