There are numerous broadcast standards. Here is a complete
overview, including details of each standard.
Many countries have already legislated in regard to compliance with specific broadcast standards, while others are still in the legislative process.
In many ways, The International Telecommunication Union's
BS.1770 recommendation is global and one of the most important
broadcast standards as many other standards are based on it. The
ITU standard concerns Broadcast Loudness and True-peak Level
measurement, and the loudness part is based on an Leq measurement
employing K-weighting, which is a specific frequency weighting
developed by the Communications Research Centre (a federal research
institute in Ottawa, Canada). This baseline method is relatively
simple, but it is based on excessive listening tests and has been
verified independently. The True-peak part of the standard was
specified by AES SC-02-01.
As mentioned, many other broadcast standards are based on ITU BS.1770, including ATSC A/85 (the US), EBU R128 (Europe), OP-59 (Australia) and TR-B32 (Japan).
In 2011, the recommendation was released in a revised version: ITU BS.1770-2 that employs a relative gate with regard to Program Loudness measurement, which was adopted from the R128 standard defined by The European Broadcast Union (EBU).
In 2012, the recommendation was updated once again to become version BS.1770-3.
ITU BS.1770 published 2006
ITU BS.1770-2 published March 2011
ITU BS.1770-3 published August 2012
The P/LOUD group, which is part of The European Broadcasting Union (EBU), has defined the R128 standard based on ITU BS.1770. However, the group also added new tools such as a relative gate that ensures even more consistent loudness across genres and types of program material. Some of these tools have been implemented in the updated version of ITU's recommendation: ITU BS.1770-3.
Basically, the R128 standard builds on 4 tech documents: EBU Tech 3341, EBU Tech 3342, EBU Tech 3343 and EBU Tech 3344.
EBU Tech 3341
This document specifies loudness metering within the R128
domain. Quite simply, a loudness meter is allowed to use the 'EBU
Mode' term if certain criteria are met. First of all, three time
scales must be available: Momentary (M), Short-term (S) and
Integrated (I) - also referred to as Program Loudness. Any
real-time 'live meter' with EBU Mode must be able to display the
three time scales, though not necessarily at the same time, and it
must also be able to display the maximum value of the Momentary
Loudness (reset when Program Loudness is being reset).
Momentary Loudness must be measured using a sliding time window of 0.4 seconds, while Short-term Loudness must be measured using a sliding time window of 3 seconds. Program Loudness must be measured using a specific gating method that excludes measurements of parts dropping below a threshold of -10 LU relative to an ungated measurement of the same program material.
Further, a meter featuring EBU Mode must also be able to display LRA (Loudness Range), which is a measurement of the variation of loudness on a macroscopic scale. This parameter is a supplement to the overall loudness measurement (Program Loudness).
The terms used for expressing the measurements are LU (Loudness Units) and LUFS, which is the same as LKFS (Loudness K-weighted Full Scale) used by other broadcast standards. The target loudness of EBU's R128 standard is -23 LUFS.
For in-depth specifications, please consult the original EBU Tech 3341 document.
EBU Tech 3342
This document specifies audio normalization based on
loudness measurements as described in EBU Tech 3342. The average
loudness level, or Program Loudness, should be used in combination
with Maximum True-peak Level and Loudness Range (LRA) to correct
program material in accordance to the R128
In essence, LRA is determined by analyzing the loudest and the softest parts of the program material. However, the lower percentile of 10% is being ignored as is the upper percentile of 95% to avoid extreme events such as a single gunshot or long passages of silence to manipulate the overall result in an undesirably way.
For in-depth specifications, please consult the original EBU Tech 3342 document.
EBU Tech 3343
This document describes guidelines for production and
implementation in accordance with EBU R128. Both Program Loudness,
LRA and True-peak metering is explained and strategies for
implementing a loudness strategy at various stages of production
For in-depth specifications, please consult the original EBU Tech 3343 document.
EBU Tech 3344
This document describes how to loudness normalize when
distributing program material to various end user platforms,
including radio, television and portable devices in various formats
such as stereo and 5.1 surround.
For in-depth specifications, please consult the original EBU Tech 3344 document.
Published August 2010
ATSC A/85 was specified by The Advanced Television Systems Committee in 2009 and applies to US broadcast digital television. A/85 is rooted in the ITU-R BS.1770 Loudness and True-peak level standard. It specifies anchor based normalization for regular programs, but all-source loudness normalization for commercials and interstitials, both at a default Target loudness of -24 LKFS. Put differently, regular programs are under a liberal, rubber-band rule, while the level of commercials is defined precisely and transparently.
A/85 includes extensive information about calibrated monitoring environments and may function somewhat like a Dolby manual. Unlike EBU R128, A/85 is only focused on the digital television platform and on the AC3 codec.
In 2011, to give the CALM Act a chance of becoming effective, two revision were published, calling for the inclusion of all sources when measuring commercials, i.e. measuring loudness rather than speech. In the original version of A/85, only the 'anchor' method was recognized. Even though the 2011 revisions were published after ITU had defined BS.1770-2, the ATSC standards ambiguously pointed to BS.1770-1, which was then no longer in effect.
From March 2013, this ambiguity has gone, because the A/85 recommended practice now prescribes ITU BS.1770-3 for all programming. Hopefully, the proprietary speech detecting measurement algorithm ATSC has come to rely on will be updated accordingly before long.
TR-B32 is a Japanese broadcast standard that builds on ITU BS.1770-2, which means that a relative gate is employed. However, the target level is -24 LUFS/LKFS as opposed to the -23 LUFS target level of the EBU R128 standard which also employs the gate. As a rule of thumb, a gated measurement of -23 LUFS/LKFS equals an un-gated measurement of -24 LUFS/LKFS.
Operational practice by FreeTV, Australia. OP-59 is rooted in BS.1770 Loudness and True-peak level and recommends a speech based as well as a universal approach to audio normalization. All short form programs should be measured using the universal (full mix) method.