User`s manual

20 / LM6 Radar Loudness Meter
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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.