Dolby Laboratories Multichannel Audio Tool DP570 - Manual (Page 102)

86 Dolby ® DP570 Multichannel Audio Tool User’s Manual
A Guide to Dolby Metadata
Special Parameters
There are professional parameters in the Dolby E bitstream that are not under direct user
control, such as Timecode and Pitch Shift.
Timecode
Dolby E bitstreams carry timecode information in hours:minutes:seconds:frames format.
Pitch Shift
The Pitch Shift parameter can be generated automatically by a Dolby E decoder to control
the Dolby Model 585 Time Scaling Processor. If the input to the Dolby E decoder is not at
normal play speed (as with varispeed or program play), then the Pitch Shift Code
parameter indicates the amount of audio pitch shifting required to restore the original
program pitch.
D.2 Dialogue Level
Dialogue Level is perhaps the single most important metadata parameter. The Dialogue
Level Set value represents the long‐term level of dialogue within a presentation, measured
according to ITU‐R Rec. BS.1770. This level can be quantified with the Dolby LM100
Broadcast Loudness Meter.
When received at the consumer’s Dolby Digital decoder, this parameter setting determines
a 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.
In broadcast transmission, the proper setting of Dialogue Level ensures that the consumer
receives a standard listening level, so switching channels or watching a television program
through the commercial breaks doesn’t require adjusting the volume. Using the same
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 and consistent listening level.
The proper setting of the Dialogue Level parameter also 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 with DVDs.
The Scale
The scale used in the Dialogue Level setting ranges in 1 dB steps from –1 to –31 dB.
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:
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.