TC Electronic LM2 Plug-in - Manual (Page 19)

LM6 - Radar Loudness Meter / 19
EN
Level versus Loudness
When level normalization in audio distribution is based on a peak level measure, it
favors low dynamic range signatures as shown in Fig 1. This is what has happened
to CD.
Quasi-peak level meters have this effect. They tell little about loudness, and also
require a headroom in order to stay clear of distortion. Using IEC 268-18 meters, the
headroom needed is typically 8-9 dB.
Sample based meters are also widely used, but tell even less about loudness. Max
sample detection is the general rule in digital mixers and DAWs. The side effect of
using such a simplistic measure has become clear over the last decade, and CD
music production stands as a monument over its deficiency. In numerous TC papers,
it has been demonstrated how sample based peak meters require a headroom of at
least 3 dB in order to prevent distortion and listener fatigue.
The only type of standard level instrument that does not display some sort of
peak level is the VU meter. Though developed for another era, this kind of meter
is arguably better at presenting an audio segment’s center of gravity. However, a
VU meter is not perceptually optimized, or ideal for looking at audio with markedly
different dynamic range signatures.
Unlike electrical level, loudness is subjective, and listeners weigh its most important
factors - SPL, Frequency contents and Duration - differently. In search of an
“objective” loudness measure, a certain Between Listener Variability (BLV) and
Within Listener Variability (WLV) must be accepted, meaning that even loudness
assessments by the same person are only consistent to some extent, and depends
on the time of day, her mood etc. BLV adds further to the blur, when sex, culture, age
etc. are introduced as variables.
Because of the variations, a generic loudness measure is only meaningful when it is
based on large subjective reference tests and solid statistics. Together with McGill
University in Montreal, TC Electronic has undertaken extensive loudness model
investigation and evaluation.
The results denounce a couple of Leq measures, namely A and M weighted, as
generic loudness measures. In fact, a quasi-peak meter showed better judgement
of loudness than Leq(A) or Leq(M). Even used just for speech, Leq(A) is a poor
pick, and it performs worse on music and effects. An appropriate choice for a low
complexity, generic measurement algorithm, which works for listening levels used
domestically, has been known as Leq(RLB).
Combined loudness and peak level meters exist already, for instance the ones
from Dorroughs, but BS.1770 now offers a standardized way of measuring these
parameters.
In 2006, ITU-R Working Party 6J drafted a new loudness and peak level measure,
BS.1770, and the standard has subsequently come into effect. It has been debated
if the loudness part is robust enough, because it will obviously get exploited where
possible. However, with a variety of program material, Leq(RLB) has been verified