Auphonic Blog: Audio Loudness Measurement and Normalization With EBU R128 (Calm Act, ATSC a:85)

7/27/2019 Auphonic Blog: Audio Loudness Measurement and Normalization With EBU R128 (Calm Act, ATSC a:85)

1/9

7/10/13 11:47 PMAuphonic Blog: Audio loudness measurement and normalization with EBU R128 (Calm Act, ATSC A/85)

Page 1 of 9https://auphonic.com/blog/2012/08/02/loudness-measurement-and-normalization-ebu-r128-calm-act/

Audio loudness measurement and normalizationwith EBU R128 (Calm Act, ATSC A/85)

Have you ever wondered why commercials sound louder than your

favorite TV shows? Or why you have to adjust the playback volume

on your television when switching between channels? The answer is

that until recently, there was no standard way to measure the per-

ceived loudness of sound recordings. Instead, audio productions

were (and still are) normalized to peak levels, which do in no way de-

termine how loud a signal is.

In this article we will discuss the EBU recommendation R128, a new

and open standard for balancing audio programs according to their

actually perceived loudness.

This recommendation marks one of the most funda-

mental changes in the history of audio in broadcast-

ing and solves a major source of irritation for televi-

sion and radio audience around the world: that of

the jump in audio levels at the breaks within pro-

grammes, between programmes and between chan-

nels (from On the Way to Loudness Nirvana).

Most big european broadcasting corporations are adapting theirworkflow to EBU R128 now, see e.g. The Loudness revolution comes

to Germany and Austria.

On the other side of the Atlantic, the same method has provided the

basis for the implementation of the CALM Act in the U.S., which is

called ATSC A/85.

See also Too many loudness standards.
http://www.atsc.org/cms/index.php/standards/recommended-practices/185-a85-techniques-for-establishing-and-maintaining-audio-loudness-for-digital-televisionhttp://en.wikipedia.org/wiki/Commercial_Advertisement_Loudness_Mitigation_Acthttp://tech.ebu.ch/news/the-loudness-revolution-comes-to-germany-03sep12http://tech.ebu.ch/news/the-loudness-revolution-comes-to-germany-03sep12http://tech.ebu.ch/loudnesshttp://www.youtube.com/watch?v=xa-8zJVuAJY&feature=relatedhttp://www.atsc.org/cms/index.php/standards/recommended-practices/185-a85-techniques-for-establishing-and-maintaining-audio-loudness-for-digital-televisionhttp://en.wikipedia.org/wiki/Commercial_Advertisement_Loudness_Mitigation_Acthttp://tech.ebu.ch/news/the-loudness-revolution-comes-to-germany-03sep12http://tech.ebu.ch/docs/techreview/trev_2010-Q3_loudness_Camerer.pdfhttp://tech.ebu.ch/loudness


2/9



What is loudness?

Loudness perception is surprisingly complicated. The physical sound

pressure level, which is usually specified in dB, tells us very little

about how loud a sound will be perceived by a listener. For example,a low-frequency tone might appear much softer than a high-frequen-

cy tone, even if it has a higher sound pressure level. This frequency-

dependency of loudness perception is described by the equal loud-

ness contours.

Figure from Wikipedia (with edits).

As if this wasn't confusing enough, the frequency dependency of

loudness perception itself varies with sound pressure level. More-

over, loudness perception is a highly subjective affair that depends on

factors such as age and possible hearing damages. In short, loudness

cannot be easily measured. Florian Camerer from the European

Broadcasting Union argues that, "there's never gonna be such a thing
https://www.youtube.com/watch?feature=player_detailpage&v=iuEtQqC-Sqo#t=302shttps://upload.wikimedia.org/wikipedia/commons/4/47/Lindos1.svghttp://en.wikipedia.org/wiki/Equal-loudness_contour


3/9



as a perfect loudness meter."

Current measurement devices and the Loudness War

Perhaps because perceived loudness is so hard to measure, it has be-come common practice to normalize audio according to peak signal

levels. This method, which we have already discussed in an article on

"Loudness Normalization and Compression of Podcasts and Speech

Audio", is driven by two somewhat incompatible concerns:

On the one hand, it is necessary to prevent clipping in digital au-

dio. For this purpose, most broadcasting stations use QPPM(Quasi Peak Programme Meters) to measure quasi peak levels

that, as we will see later, can actually lie below the 'true peaks'.

These quasi peaks are then normalized to -9 dBFS (see p.2).

But at the same time, peak normalization has been used as a

method for maximizing the loudness of an audio program, de-

spite the fact that peaks do in no way determine how loud a sig-nal is perceived. The actual loudness of a peak-normalized pro-

gram is therefore entirely unpredictable, which can cause annoy-

ing inconsistencies at transition points.
http://tech.ebu.ch/webdav/site/tech/shared/techreview/trev_2010-Q3_loudness_Camerer.pdfhttps://en.wikipedia.org/wiki/Peak_programme_meterhttp://en.wikipedia.org/wiki/Clipping_(audio)http://auphonic.com/blog/2011/07/25/loudness-normalization-and-compression-podcasts-and-speech-audio/https://www.youtube.com/watch?feature=player_detailpage&v=iuEtQqC-Sqo#t=302s


4/9



Loudness inconsistencies due to peak

normalization. Figure from "On the

way to Loudness nirvanaaudio lev-

elling with EBU R 128" (p.1).

Because there was no loudness refer-

ence level, producers were worried

that their productions would not ap-

pear as loud as everybody else's. In

addition to peak normalization, they

therefore used more and more dy-namic range compressors and hard limiters to maximize the loud-

ness (and thus allegedly the impact) of their programs. As a result of

this Loudness War, the dynamic range of professional audio produc-

tions consistently shrank over recent decadesand with it arguably

their expressivity.

A new and open loudness measure (ITU-R BS.1770, EBU R128)

Over time, it became increasingly obvious that a unified reference

was required to normalize different audio programs to the same per-

ceived loudness. An early attempt in this direction was ReplayGain

from 2001. Five years later, the International Telecommunication

Union introduced the more sophisticated ITU-R BS.1770 standard. Itsspecification is about as intuitive as its name, but suffice it to say that

the standard describes an efficient and open algorithm for loudness

and peak level measurement:
http://www.itu.int/dms_pubrec/itu-r/rec/bs/R-REC-BS.1770-2-201103-I!!PDF-E.pdfhttp://replaygain.org/http://en.wikipedia.org/wiki/Loudness_warhttp://tech.ebu.ch/docs/techreview/trev_2010-Q3_loudness_Camerer.pdf


5/9


6/9



In 2011, the European Broadcasting Corporation proposed an exten-

sion to the ITU standard called EBU R128, which uses three parame-

ters to characterize an audio signal:

The program loudness in LUFS specifies how loud a program ison average from its beginning to its end.

In order to prevent clipping, the standard suggests a maximum

true peak level of -1 dBFS for PCM, or lower levels for certain

parts of the transmission chain (e.g., lossy or low-bitrate codecs,

analogue re-broadcasters). ITU-R BS.1770 suggests to use an over-

sampling peak meter to measure the true peaks that can lie be-tween samples and are often higher than the peaks shown by a

QPPM or sample peak meter.

The 'true peaks' of a digital audio signal can lie between its sam-ples. Figure from ablog by Morten Eriksen.

The loudness range (LRA) indicates the variation of loudness

over the course of a program and is measured in LU. It can be

used to determine whether a production requires dynamic treat-

ment and how to adapt it to different distribution channels. For

example, an audio signal with a large LRA might need to be com-
http://tech.ebu.ch/webdav/site/tech/shared/tech/tech3342.pdfhttps://morteneriksen.wordpress.com/tag/cubase/http://www.hometracked.com/2007/11/08/prevent-intersample-peaks/http://en.wikipedia.org/wiki/Clipping_(audio)http://tech.ebu.ch/loudness


7/9



pressed, and podcasts generally require a lower LRA than classi-

cal music recordings.

Loudness distribution and LRA for the film 'The Matrix'. Figure from

EBU Tech Doc 3343 (p.13).

Loudness normalization with EBU R128

So what are the practical implications of all this stuff for audio pro-

duction? Well, the EBU standard provides us with the means to nor-

malize an audio production to an actually perceived loudness andpunishes the tendency towards overcompression that stemmed from

the practice of peak level normalization. In the words of Florian

Camerer (p.2):

The fight for "Who is the loudest" disappears, mixes can be more

dynamic, there are fewer dynamic compression artefacts, such as

"pumping", and thus there is an overall increase of audio quality!
http://tech.ebu.ch/webdav/site/tech/shared/techreview/trev_2010-Q3_loudness_Camerer.pdfhttp://tech.ebu.ch/webdav/site/tech/shared/tech/tech3343.pdf


8/9



The EBU standard proposes -23 LUFS as the new center of the audio

levelling universe (p.4), a meaningful target loudness that all audio

content should be normalized to. However, Auphonic still uses a

higher loudness target as default (EBU R128, ATSC A/85 and other

common targets are selectable), which is discussed in Loudness Tar-gets for Mobile Audio, Podcasts, Radio and TV.

For more detailed information about EBU R128, watch the introduc-

tion by Florian Camerer:

Summary

To wrap up, let's briefly summarize the problem:

Loudness perception does not directly correspond to signal level.

Peak normalization therefore results in unpredictable loudness

levels.

To counteract fears of not appearing as loud as everybody else,producers therefore got engaged in a Loudness War, in which

most dynamics were lost to overcompression.

... and its solutions:

Loudness normalization is concerned with balancing audio pro-

grams according to their actually perceived loudness.The ITU-R BS.1770 and EBU R128 standards provide an algo-

rithm for quantifying the loudness and loudness range of a given

audio program in loudness units (LU or LUFS).

Broadcasting corporations and Auphonic are adapting their

workflow to EBU R128 and ATSC A/85 now, to predictably bal-

ance the loudness of their programs. This counteracts the tenden-cy to overcompress.
https://auphonic.com/blog/2013/01/07/loudness-targets-mobile-audio-podcasts-radio-tv/http://tech.ebu.ch/webdav/site/tech/shared/techreview/trev_2010-Q3_loudness_Camerer.pdf


9/9



Documents

Auphonic Blog: Audio Loudness Measurement and Normalization With EBU R128 (Calm Act, ATSC a:85)