Dolby Laboratories DP564 - Manual (Page 75)

DP564 Multichannel Audio Decoder Appendix A: Metadata
A-5
When received at the consumer’s Dolby Digital decoder, this parameter setting
determines the level shift in the decoder that sets, or normalizes, the average audio
output of the decoder to a preset level. This aids in matching audio volume between
program sources.
The proper setting of the dialogue level parameter enables the Dynamic Range
Control profiles chosen by the content producer to work as intended in less-than-
optimal listening environments, and is essential in any content production, whether it
is for transmission in a broadcast stream or for direct distribution to consumers, as in
DVDs.
In broadcast transmission, standard setting of dialogue level ensures that the
consumer can switch channels or watch a television program without having to adjust
the volume control during commercial breaks. Using that standard for all content,
whether conveyed by broadcast television, DVD, or other media, enables the
consumer to switch between sources and programs while maintaining a comfortable
listening level.
Note: Programs without dialogue, such as an all-music program, still require a
careful setting of the dialogue level parameter. When setting the parameter for
such content, it is useful to compare the program to the level of other
programs. The goal is to allow the consumer to switch to your program
without having to adjust the volume control.
The Scale
The scale used in the dialogue level setting is from –1 to –31 dB in 1 dB steps.
Contrary to what you might assume at first, a setting of –31 represents no level shift
in the consumer’s decoder, and –1 represents the maximum level shift. Here’s why:
Dolby Digital consumer decoders standardize the average loudness (averaged over
time by the formula LeqA) to –31 dBFS (31 dB below 0 dB full-scale digital output)
by applying a shift in level based on the dialogue level parameter setting. When a
decoder receives an input signal with a dialogue level setting of –31, it applies no
level shift to the signal because this indicates to the decoder that the signal already
matches the target level and therefore requires no shift. In contrast, a louder program
requires a shift to match the –31 dB standard. When the dialogue level parameter
setting is –21, the decoder applies a 10 dB level shift to the signal. When the setting is
–11, it applies a 20 dB level shift, and so on.
A Simple Rule:
31 + (dialogue level value) = Shift applied
Example:
31 + (–21) = 10 dB