Grass Valley Imagestore 750 v.2.0.1 - Manual (Page 336)

Dolby Decode/Encode Imagestore 750 User Manual
Page 336 Miranda Technologies Inc.
Dolby Digital (AC3)
Dolby Digital is a process used to carry multi-channel audio in a stereo audio
signal. This is sometimes termed “AC3”, after the coding technology used.
The high quality compression achieved takes advantage of human hearing.
Resulting decoded audio is not meant for re-encoding, rather for listening;
hence its use in transmission. The Dolby Digital bitstream is a transmission
bitstream, intended for delivery to the consumer at home.
Dolby E
Dolby E is a high quality, video frame-synchronized audio compression
coding system which enables broadcasters to distribute surround sound and
multi-lingual audio using an existing stereo infrastructure. Up to eight audio
channels plus metadata can be carried on a stereo channel. Dolby E can
tolerate multiple encode/decode cycles encountered during broadcast
contribution, post-production and distribution stages. Dolby E Encoders and
Decoders convert to/from compressed audio.
Dolby Metadata
A Dolby data-stream contains information about the Dolby-encoded audio
bit-stream itself – called metadata. Metadata is different for Dolby Digital
and Dolby E. It is used to control aspects of the audio decoding and
reproduction.
Dolby E metadata contains Dolby Digital metadata for every audio program
carried in the Dolby data-stream, plus information on the transport stream.
Dolby Digital metadata contains data to be used by consumer electronics.
The metadata is a list of various parameters, for example:
•
Audio Coding Mode – describes a program’s associated audio
channels.
•
Dynamic Range – used to compress audio dynamic range at the
consumer equipment for, say, late night viewing.
•
Dialog Normalisation – adjusts consumer equipment audio output
for consistent viewer loudness; for example, across commercials,
films, local news.