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From: Stormiy on 8 Jul 2010 11:09

Im implementing ITU standard based loudness measurement program and as it
states i should use some kind of gating to exclude silence regions from
affecting measured average sound level - for example - Ill take general
integration time of 3 seconds - if, for example the first second of whole
sound contains speech and the last 2/3 of it contains silence (people
taking breath, thinking or for similar reasons) then value of loudness i
get is smaller than it should be - because im taking silence regions in
account. So then there is somehow suggested, but not very well documented
solution - you take "instant" (400ms) loudness measurement besides needed
(3000ms) integration time and if "instant" loudness is 8LU (LU stands for
Loudness Unit) lower than loudness measured in "full time"(3000ms) - you
then pause loudness measurement, while you get your instant level in range
of long range level. Long story short - you get a number of incoming
samples, for example 10ms of them, you calculate your sliding short and
long term loudness, then you compare if the short term loudness is 8 units
lower than long term and discard that set of samples/pause sound
measurement for 10ms samples you just got, effectively ignoring them and
keeping your long term loudness in higher level - ignoring those 10ms that
are "to silent relative to long term";

So the problem is: since im ignoring all the samples(small chunks of
samples actually) that are 8lu lower than my long term loudness level, im
effectively blocking my long term loudness level to become smaller when it
actually should.

From "2010 papers of EBU P/Loud working group:

"P/LOUD conducted listening tests in Q4/2009 and January 2010 to determine
the best gating threshold. It was found that two candidate gating methods
out of the four tested gave good results, both being statistically
significantly better than the other two. Those two methods were a gate of
6LU relative to ungated LKFS ('6rel') and 10LU relative to ungated LKFS
('10rel'). For all candidates a block length of 400ms was used.
Pragmatically, a value of 8rel was chosen for further informal tests
against the other gating function already used by broad‐casters"*

P.S Sorry for my En, its not my native language.



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