The broadcast industry inspired the development of the LUFS meter because of the growing increase in the
loudness of advertisement audio compared to television program audio.
INTRODUCING LUFS
And to the rescue came Loudness Units
relative to Full Scale (LUFS). LUFS equate the
perceived loudness of one production with
the perceived loudness of another. Designed
for the broadcast industry, and established in
2011/2012, a LUFS meter facilitates loudness
normalization.
Most of us are familiar with peak normalization
or level normalization, which adjusts the digital
level of a waveform so that the peak levels
all reach a maximum dBFS reading—often 0
dBFS, but several normalization plug-ins let the
user select any maximum level.
Loudness normalization is like level
normalization in a way, but lets the user set
a perceived loudness level for the audio
waveform. RMS level—the level measured by a
VU meter—provides an average level measured
over a span of a few hundred milliseconds.
It equates closer to perceived loudness and
doesn’t contain peak readings.
The beauty of the LUFS reading is that it
measures the difference between the average
(RMS) level and the peak level. It legitimately
takes into account the peak and average
levels. Upon much ponderance, most folks
could see how the closer that average level
gets to the peak level, the louder the audio
will sound! The LUFS reading is in negative
numbers and -12 LUFS simply indicates that
the average perceived loudness is 12 dB below
the peak level. So, given a common peak level
of 0 dBFS, it makes sense that a waveform that
reads -24 LUFS would sound a lot quieter than
a waveform that reads -8 LUFS, even though
both waveforms have the identical peak level!
GET YER LUFS HERE!
You might say, “Well Bill, how do I get me some
o’ them LUFS?” At the root of the volume wars
is the peak limiter. Peak limiters have a superfast
attack time that’s capable of catching all
of the transient content and keeping it from
exceeding the threshold. It also has a fast
release time so that it can recover quickly
enough to stop the next transient. Peak limiters
are different than normal compressors because
there’s no practical need to adjust the attack or
release time. Most peak limiters, such as the
Waves L1, L2, and L3 Ultramaximizers, have
two sliders: one that pushes the audio signal
up into the threshold (essentially turning the
average level up while increasingly limiting the
peaks) and another that sets the peak level.
Mastering engineers have been using peak
limiters for a long time to set the mastered
loudness level. There’s a lot more that goes into
a great mastering job, but once everything else
is set, the peak limiter is a tool that can help find
the desired LUFS setting. Insert a LUFS meter
at the end of your signal chain, just before the
LUFS meter, and use the threshold of a peak
limiter to push and pull the mix level to and
from the threshold until you find the setting that
results in your target LUFS reading.
But there evolved a problem. Once musicians
and engineers figured out that a peak limiter
could help their music sound louder, it was
like giving kids the keys to the candy shack!
They stopped leaving it to chance—or to
the discretion of an experienced and wise
mastering engineer. Instead of leaving at
least a few dB of headroom and trusting the
mastering engineer to choose the perfect final
processing, engineers and producers started to
do their own backend processing. This caused
mastering engineers to start complaining that,
by the time they received the audio files, they
were already way over limited.
WHAT’S A TRUE PEAK?
There’s another concern that accompanies
loudness normalization called the true peak
level. When your digital audio data is finally
converted to analog audio waves (so the listener
can hear it) the DAC redraws the waveform as
smoothly as possible. If a few samples have
clipped—or are legitimately all at 0 dBFS—the
waveform is drawn with a rounding peak that
exceeds 0 dBFS. This is called inter-sample
distortion, and is problematic in that it isn’t
visible on the final output on a dBFS meter but
it needs to be dealt with because inter-sample
distortion can overdrive consumer playback
devices, causing them to distort, even though
the dBFS meter doesn't show any clipping or
overs.
Most meters that read LUFS contain a True
Peak meter that can read and limit theses
problematic levels. Turn on the True Peak limiter
and set it to limit these peaks at least by 1 dB
True Peak (dBTP). Some mastering engineers
and streaming services prefer to limit these
peaks by 2 or 3 dBTP.
It’s also important to note that these True Peaks
aren’t necessarily caused by audio data that is
corrupt or distorted, so simply lowering the level
or the digital to analog bounce by 1–3 dB could
solve the problem; however, this fundamental
adjustment would also affect the perceived
loudness of the file. Most engineers prefer to
provide their best mix and limit the True Peaks
in the final stage of mastering.
HOW MANY LUFS ENOUGH
Okay, I know, you’re probably saying, “Bill.
O.M.G.! I get it! LUFS might be the single most
important audio topic of 2020! HOW MANY
August 2020
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