TC Electronic SYSTEM 6000 MKII, Руководство по алгоритмам

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lM6
Introduction
Since 1998, TC has performed listening tests and evaluation of loudness models; and therefore holds an extensive,
Universal Database of loudness, based on ten thousands of assessments. The database covers all sorts of broadcast
material, music, commercials, feature film and experimental sounds, and is verfied against other independent studies.
Fig 1.
Left: DRT for consumers under different listening situations
Right: Peak level normalization means that material targeted low dynamic range platforms gets loud.
The Universal Database is authoritative from an
academic as well as a practical point of view. It has been
indispensable when designing the LM6 meter, because it
provided the missing link between short-term and long-term
loudness, and enabled the statistically founded Universal
Descriptors of LM6 .
The chart of Dynamic Range Tolerance in Fig 1 is a
side-effect of the studies mentioned: Consumers were
found to have a distinct Dynamic Range Tolerance (DRT)
specific to their listening environment. The DRT is defined
as a Preferred Average window with a certain peak level
Headroom above it. The average sound pressure level,
which obviously is different from one listening condition to
another, has to be kept within certain boundaries in order
to maintain speech intelligibility, and to avoid music or
effects from getting annoyingly loud or soft.
Audio engineers instinctively target a certain DRT profile
when mixing, but because level normalization in broadcast
and music production is based on peak level measures,
low dynamic range signatures end up the loudest as shown
by the red line in Fig 1, right. Audio production is therefore
trapped in a downwards spiral, going for ever decreasing
dynamic range. By now, the pop music industry is “right of”
In Flight Entertainment in the illustration.
LM6 offers a standardized option: The visualization of
loudness history and DRT in combination with long-term
descriptors from production onwards, is a transparent
and well sounding alternative to our current peak level
obsession. Not only for music, but also in production for
broadcast or film. The engineer, who may not be an audio
expert, should be able to identify and consciously work
with loudness developments within the limits of a target
distribution platform, and with predictable results when the
program is transcoded to another platform.
LM6 therefore color codes loudness so it’s easy to identify
target level (green), below the noisefloor level (blue), or
loud events (yellow), see Fig 2.