Perceived Loudness (EBU R 128)
The specification EBU R 128 / ITU-R Bs.1770-4 describes an algorithm for calculation of the perceived loudness of real world audio signals, for example no pure sine tones.
For details of the recommendations please see EBU R128 Loudness normalisation and permitted maximum level of audio signals.
LUFS
k frequency weighting function
EBU R 128 loudness is:
- measured in LUFS (Loudness Units Full Scale, or equivalently LKFS, Loudness k-weighted Full Scale) for absolute values or LU (Loudness Units) for relative values, whereat 0 LUFS are equivalent to full scale.
- The loudness is defined as the k-weighted (see Filter Curve EQ or Graphic EQ) sum of the squared values of all channels, in which the k-weighting
approximates
the characteristics of the human ear. Thus, LU are somewhat related to the mean square without root. - Usually, the perceived loudness
is calculated in
blocks of 400 milliseconds every 100 milliseconds** (so called momentary loudness). - LU's
are defined
from a physical point of view that multiple audio sources add up within air and thus the loudnessincreases by
adding another audio source. A consequence of the LU definition is that the amplitude of multi-channel audiodecreases if
another channels is addedwhile
the loudness is kept constant.
Multi-channel audio
In multi-channel audio, the individual channels are weighted before adding them to the total loudness.
In Audacity's case which supports only mono and stereo tracks at the time of writing, all channels have equal contribution.
LU's are defined from a physical point of view that multiple audio sources add up within air and thus the loudness increases by adding another audio source. A consequence of the LU definition is that the amplitude of multi-channel audio decreases if
another channels is added while
the loudness is kept constant. While this point of view is completely valid it causes problems together with all known PC audio drivers. Those drivers simply double mono signals that are played on stereo speakers without attenuating
their value which results in
the double playback loudness. To compensate this, Audacity's Loudness Normalization effect has an option to take this loudness doubling into account.
Integrative loudness and loudness gating
Loudness gating example
标签:Perceived,Bs.1770,EBU,LU,Loudness,128,loudness,Audio,audio From: https://www.cnblogs.com/abaelhe/p/18470574Since the perceived loudness is
mostly determined by
the louder parts of a track,
an accurate loudness measurementhas to ignore
quier or even silent parts.
Thisis realized by
loudness gating.
- First, loudness gating as defined by EBU R 128
discards
all measurement blocks that are below an absolute threshold of -70 LUFS(grey in the example
histogram, the large peak in the lowest bin iscaused by
silence at the start and end of the track).- In the next step, a relative threshold
is calculated
10 LU below the average of the blocks above -70 LUFS(red in the example
histogram). All blocks below that relative thresholdare discarded as well
.- Finally, the perceived loudness
is calculated as
the average of the remaining blocks (blue in the example
histogram).