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Frequently Asked Questions
Q. Doesn’t Dolby Digital (AC-3) already
contain dynamic range control features?
A: Yes, and no. Dynrng and compr, known collectively as DRC do provide
some degree of gain control but there are three large problems. First,
DRC must either be set in metadata and then delivered all the way to the
Dolby Digital (AC-3) encoder, or more than likely a preset is chosen
within the Dolby Digital (AC-3) encoder. Second, in order for DRC to
function properly, dialnorm must be set correctly, and this also
requires a working and accurate metadata path. Third, all of the default
presets currently contain a “null zone” that can be several dB wide.
Within this zone no gain reduction takes place, and therefore loudness
shifts between programming and commercials will pass through untouched.
Again, with properly set metadata, this issue can be minimized.
Q: OK, then which terrestrial networks are sending metadata to their
affiliates?
A: Many terrestrial networks are sending metadata to their affiliate
stations (see the Station Notes section of this website), however this
data is only present and proper during network programming. At other
times, the Dolby Digital (AC-3) encoders are operating with default
metadata values. This may be OK for some programming, but it is very
likely allowing annoying loudness shifts to be transmitted to consumers
especially during local insertions.
Q: Doesn’t dynamic range processing defeat the DRC functionality of
Dolby Digital?
A: No, not at all. When setup correctly, the Linear Acoustic OCTiMAX 5.1
will do as little processing as the station desires while still
monitoring the audio to protect against incorrect or missing metadata,
stepping in only when necessary.
Q: Isn’t a 5.1 channel audio processor the same as three 2-channel
processors?
A: Actually, it is not even close (and we tried it!). After two years of
research and multiple US and foreign patent applications, we developed
an algorithm specifically for multichannel audio.
Q: Can it help with other local audio issues?
A: The OCTiMAX 5.1 contains inputs for local station and voiceover
audio. These inputs can be used for a voiceover of the main 5.1 or
2-channel program as well as a switched feed which, via a simple GPI
contact closure, will switch between network and local audio. The unit
also contains the upMAX™ upmixing process to allow local stereo, mono,
and surround encoded content to be selectively and accurately turned
into a 5.1 channel surround-field. This allows local content to
spatially match network delivered content, importantly keeping dialogue
in the center channel. It also provides a solution for the stereo to 5.1
switching artifact that occurs in some consumer decoders.
Q: Can the OCTiMAX 5.1 be used with existing analog services?
A: Yes. As the OCTiMAX 5.1 can be set to independently process eight
mono channels, four stereo pairs, a 5.1 channel plus a stereo, or any
combination in between, the unit can replace multiple less powerful
units and be ready for the future. For example, one OCTiMAX 5.1 can be
used to pre-process an analog NTSC feed and multiple cable feeds with
each one getting as much or as little processing as needed. External
pre-emphasis and stereo generation is still required, and can be
obtained from Modulation Sciences, Orban, and others.
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