Dolby Laboratories DP570 - Manual (Page 104)

92 Dolby ® DP570 Multichannel Audio Tool User’s Manual
A Guide to Dolby Metadata Parameter Definitions
stream to either a downstream decoder or an integrated amplifier with Dolby Digital
decoding.
In each of these devices, the analog stereo output is one of two different stereo downmixes.
One type is a stereo‐compatible Dolby Surround downmix, of the multichannel source
program that is suitable for Dolby Surround Pro Logic
® decoding. This kind of downmix
is also called Pro Logic or Left total/Right total (Lt/Rt). The other type is a simple stereo
representation (called Left only/Right only, or Lo/Ro) suitable for playback on a stereo hi‐fi
or on headphones, and from which a mono signal is derived for use on an RF/Antenna
output. The difference between the downmixes is how the Surround channels are handled.
The Lt/Rt downmix sums the Surround channels and adds them, in‐phase to the Left
channel and out‐of‐phase to the Right channel. This allows a Dolby Surround Pro Logic
decoder to reconstruct the L/C/R/S channels for a Pro Logic home theater. The Lo/Ro
downmix adds the Left and Right Surround channels discretely to the Left and Right
speaker channels, respectively. This preserves the stereo separation for stereo‐only
monitoring and produces a mono‐compatible signal. In all downmixes, the LFE channel is
not included.
On most home equipment, the consumer can use the product’s user interface to choose the
appropriate stereo output for his playback system. The mono signal feeding the
RF/Antenna output is usually derived from the Lo/Ro downmix.
There are separate metadata parameters that govern the Lo/Ro and Lt/Rt downmixes.
Certain metadata parameters allow the engineer to select how the stereo downmix is
constructed and which stereo analog signal is preferred, but Lt/Rt is the default selection
in all consumer decoders. See
Parameter Definitions on page 92 for the definition of
individual parameters.
During downmixing, as we have seen, the adjustment of Dynamic Range Control
parameters is limited. Broadly speaking, the stereo outputs use the Line mode compression
profile while the mono signal uses RF mode compression. As with dynamic range control,
downmixing is ultimately dependent upon each consumer’s unique listening
environment.
While the engineer must optimize the multichannel mix for reproduction in an ideal
listening environment, it is also important to preview the mix in downmixing conditions
to ensure compatibility with different playback systems when selecting the downmixing
metadata parameters. These previews can be achieved in real time using the DP570
Multichannel Audio Tool.
D.6 Parameter Definitions
This section explains both professional and consumer metadata parameters in greater
detail.
Metadata parameters include:
• Universal parameters
• Extended Bitstream Information (Extended BSI) parameters
Extended BSI parameters are active only when both the producer chooses to use them and
the consumer’s decoder is capable of reading them. All decoders can successfully decode a