Owner manual

LM5/LM5D & AM6 -TDM / 15
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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.