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Linear Acoustic LA-5180 Metadata Frame Sync/Generator Operation Manual
can then be kept as baseband with metadata being inserted into the VANC space. The au-
dio then leaves the postproduction studio in either baseband or compressed form and is
passed through the plant to Master Control. The audio program that is selected by master
control plus its associated SAP or Visual Descriptive audio (if present) is sent to the trans-
mission audio processor (such as the Linear Acoustic AEROMAX 5.1) which accept base-
band audio and the Professional Metadata stream and encode the audio program according
to its associated metadata.
Finally, the signal is decoded in the consumer's home, with metadata providing the infor-
mation for that decoding process. Through the use of metadata, the mixer in the truck has
been able to control the home decoder for the sporting event, while news breaks, commer-
cials, station IDs, and the like are similarly appropriately decoded due to their pre-existing
metadata.
7.4.2
Theatrical Movies for Broadcast
This situation is probably the most straightforward, as multichannel audio and metadata
have been part of film transfers since the first laser disc was released with a Dolby Digital
(AC-3) soundtrack in the early 1990's. Film mix stages went through a transformation in
the mid 1970's when Dolby Stereo was introduced. A large and ongoing effort was begun
in order to standardize the film mixing process and mixing levels so that the soundtrack
would play back consistently from one facility to another and from the final mix stage to
the theatre. Dialog loudness was chosen as the anchor or reference for the soundtrack, and
speaker positions and calibration levels were carefully chosen. Today it is possible to start
a project at one facility, finish it at another, and release a film with confidence that it will
play properly in theatres. This consistency has greatly simplified the task of transferring
film to video, especially films with multichannel audio. Picking the correct metadata values
is very straightforward, and it is likely that a preset group of values like the ones shown in
the table at the end of this document will work in virtually every situation. However, there
are a few things that should be kept in mind:
•
If the film is simply being edited for television and there is no re-mixing, the dialnorm
value will most likely fall in the -27 to -31 range. If the soundtrack is re-mixed to a dif-
ferent reference level, the dialnorm value will be different and should be re-measured.
Currently, the simplest way to do this is with a Dolby LM100 or a DP570.
•
Film mix stages are aligned to 85 dB Sound Pressure Level (SPL) and generally use
large horn-loaded theatre speakers. This translates well to theatres, but not so well to
home environments. It is strongly recommended that for television transfers that
smaller speakers with dome-type HF drivers be used and that the room be calibrated
to around 79 dB SPL; 78-80 dB SPL is typical. Smaller speakers and lower levels has
revealed some very interesting mistakes on film soundtracks that have been corrected
prior to the DVD release.
•
Unlike consumer systems where all main speakers are calibrated for equal SPL, film
soundtracks are mixed in environments where the SPL of the surround speakers is 3dB
46
Metadata
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