TC Electronic Radar Meter Bundle TDM - Manual (Page 17)

LM5/LM5D & AM6 -TDM / 15
ENGLISHENGLISH
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).
In 2006, ITU-R Working Party 6J drafted a new loudness and peak level measure,
BS.1770-2, 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
in independent studies to be a relatively accurate measure, and correlate well with
human test panels. It therefore seems justified to use Leq(RLB) as a baseline measure
for loudness, especially because room for improvement is also built into the standard.
The final BS.1770-2 standard included a multichannel annex with a revised weighting
filter, R2LB – now known as “K” weighting - and a channel weighting scheme.
These two later additions have been less verified than the basic Leq(RLB) frequency
weighting.
The other aspect of BS.1770-2, the algorithm to measure true-peak, is built on solid
ground. Inconsistent peak meter readings, unexpected overloads, distortion in data
reduced delivery and conversion etc. has been extensively described, so in liaison
with AES SC-02-01, an over-sampled true-peak level measure was included with
BS.1770-2.
In conclusion, BS.1770-2 is an honorable attempt at specifying loudness and peak
level separately, instead of the simplistic (sample peak) and mixed up measures
(quasi-peak) in use today. The loudness and peak level measurement engine of LM5D
follows the standard precisely. Possible updates to the ITU standard may be released
as LM5D updates.
Technical papers from AES, SMPTE, NAB and DAFX conferences with more
information about loudness measurement, evaluation of loudness models, true-peak
detection, consequences of 0 dBFS+ signals etc., are available from the TC website.
Visit the Tech Library at www.tcelectronic.com/techlibrary.asp for details.