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LM6
English Manual (2014-03-05) 61
Meter Calibration
Because of the frequency and channel weight-
ing, and of the way channels sum, only specific
tones and input channels should be used for
calibration.
The most transparent results are obtained us-
ing a 1 kHz sine tone for calibration. Other fre-
quencies or types of signal may be used (square
wave, noise etc.), but don’t expect similar results.
The beauty of the system lies in its RMS founda-
tion, so this is a feature, not an error. The same
feature enables the loudness measure to identify
overly hot CDs or commercials, and to take out-
of-phase signals into account just as much as
signals that are in phase.
If we stick to standard methods for measuring
peak audio level in a digital system, where a sine
wave (asynchronous of the sample rate) with dig-
ital peaks at 0 dBFS, is regarded a 0 dBFS tone,
BS.1770 and LM6 output these results:
– One front channel fed with a -20 dBFS, 1 kHz
sine tone: Reading of -23,0 LUFS.
–
Two front channels fed with a -20 dBFS, 1 kHz
sine tone: Reading of -20,0 LUFS.
– All 5.1 channels fed with a -20 dBFS, 1 kHz
sine tone: Reading of -15,4 LUFS.
Display
LM6 may use either the measurement unit of LU
(Loudness Units) or LUFS (Loudness Units Full
Scale).
LU and LUFS are measurements in dB, reflect-
ing the estimated gain offset to arrive at a certain
Reference Loudness (LU) or Maximum Loudness
(LUFS) as defined in BS.1770. Since a common
reference point for LU has not been agreed on
at the time of writing, LUFS (or “LKFS”, point-
ing specifically to the Leq(R2LB) weighting of
BS.1770), might be favored initially to avoid am-
biguous use of the term LU.
The effectiveness of any loudness meter de-
pends on both the graphical appearance and dy-
namic behavior of its display, as well as on its un-
derlying measurement algorithms. A short-term
loudness meter also relies on the measurement
algorithm’s ability to output pertinent loudness
information using different analysis windows, for
instance, 200-800 ms for running real-time up-
dates.
It should be noted how the optimum size of this
window varies from study to study, possibly be-
cause the objective of a running display hasn’t
been fully agreed upon.
Formal evaluation of a visualization system is
challenging. First of all, one or more metrics
must be defined by which the display should
be evaluated. The correspondence between the
sound heard and the picture seen is one aspect
to be evaluated. Another metric could character-
ize the speed of reading the meter reliably.
In TC Electronic LM2, LM5 and LM6, short-term,
mid-term and long-term of loudness measure-
ments are tied together coherently, and dis-
played in novel ways (angular reading and radar)
that were preferred in its development and test
phases. However, we remain open to sugges-
tions for further improvement of the visualization
of loudness.
Postscript
Control of loudness is probably the only audio is-
sue that has made it to the political agenda. Po-
litical regulation is currently being put into effect
in Europe to prevent hearing damage and distur-
bances from PA systems, and to avoid annoying
level jumps during commercial breaks in televi-
sion. In Australia, something similar may happen.
Many years of research into loudness of not only
dialog, but also of loudness relating to any type
of audio programming, has brought TC to the
forefront of companies in the world to perform
real-time loudness measurement and control.
Therefore, TC has taken active part in loud-
ness standardization efforts in Japan, the United
States, Europe and other areas.
In broadcast, digitization is driving the number
of AV channels and platforms up, while the total
number of viewers remains roughly the same. On
the sound production side, it is therefore impor-
tant that delivery criteria can be easily specified
and met, even by people not primarily concerned
with audio: Journalists, musicians, video editors,
marketing professionals etc.
Using only dialog based audio measurements
in digital broadcast, has led to ambiguous level
management, more level jumps between pro-
grams, and extra time spent on audio produc-
tion and management in general. Non-dialog
based level jumps are currently creating havoc