TC Electronic SYSTEM 6000 MKII Algorithm Manual

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lM6
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 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, 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.
In conclusion, BS.1770 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 LM6 follows the standard precisely.
PossibleupdatestotheITUstandardmaybereleasedas
LM6updates,providedthatprocessingrequirmentsdoesn’t
exhaust the system.
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.
Meter Calibration
Because of the frequency and channel weighting, and
of the way channels sum, only specific tones and input
channels should be used for calibration.
Themosttransparentresultsareobtainedusinga1kHz
sine tone for calibration. Other frequencies 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 foundation, 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digital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.
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 in
independent studies to be a relatively accurate measure,

TC Electronic SYSTEM 6000 MKII Specifications

General

Brand	TC Electronic
Model	SYSTEM 6000 MKII
Category	Computer Hardware
Language	English