TC Electronic DB4 MKII - Manual (Page 12)

MDX 5.1
8 DB4 / DB8 MKII Algorithms
The jumping level problem from analog TV will
become bigger if stations transmit feature films
with a less suitable dynamic range than today,
because film fall way outside the Dynamic Range
Tolerance of the average consumer under her
domestic listening conditions.
Consequently, dynamic range restriction must
take place either at the station, or inside the con-
sumer’s receiving device.
Dynamic range translation should deal with both
overly soft and overly loud parts. Ideally, the per-
fect re-mapping should happen at the receiving
end to accommodate a wide range of listening
conditions. Metadata in conjunction with, for in-
stance, Dolby AC3, provides some of these ca-
pabilities. However, even if the consumer knows
how to adjust the dynamic range of a film to her
current listening conditions, the optimum dy-
namics treatment unfortunately far exceeds the
capabilities of an AC3 decoder. The dynamic
range control in the codec is acceptable for cut
and boost ranges of 4 to 6 dB, but preparing a
feature film for broadcast needs considerably
more than this.
If such a large correction is left only to the
AC3 decoder, the wide-band gain changes can
be quite audible. Film and music dynamic range
correction requires a multiband structure so lis-
teners don’t sacrifice speech intelligibility, or get
subjected to the spectral intermodulation of a
crude, wideband range controller.
MDX 5.1
The MDX 5.1 processor available in DB4 and
DB8 is capable of bringing up low level detail,
rather than boosting everything, and then having
to limit the transients afterwards, see Fig 2. Low
level lift can even be applied to specific channels
selectively in one, two or three frequency bands.
Fig 2.
DXP processing vs. traditional Compression
and Limiting. Note how already loud signals are
unnecessarily affected when relying on limiting
and clipping.
Applications
MDX 5.1 is well suited for dynamic range control
of any kind of broadcast material. Film, sports,
music or game shows. It may be applied during
ingest, transmission – or both places.
With suitable parameter settings, high resolu-
tion audio can pass through more than one hun-
dred MDX 5.1 processors without perceivable
degradation of quality The ingenious topology
of DB4 and DB8 allows for the processing to
be performed instantly (the latency is below 0.5
ms, equivalent to moving a microphone approxi-
mately 16 cm or 6 inches), making re-alignment
of audio and picture a non-issue.
Processing strategies
The major part of dynamic range translation
should be done at the station, leaving only small-
er corrections to be performed at the consumer.
This ensures competitive audio with regards to
consistency, quality and speech intelligibility,
and prevents asking more from the AC3 decoder
than it can deliver in a civilized manner.