POST



Loudness

Across Europe from 2012 onwards, broadcasters have started to adopt and roll out sound mixing and measurement to the new EBU R.128 recommendation.

The extreme changes in programme loudness when a viewer changes channel, or the jump in audio between programmes and commercials, has been one of the most common causes of complaints to broadcasters for years. 

Across Europe from 2012 onwards, broadcasters have started to adopt and roll out sound mixing and measurement to the new EBU R.128 recommendation, which tackles the challenges of consistent programme loudness across a channel.

The EBU R.128 recommendations have introduced three parameters of sound measurement, that are carried out simultaneously: the True-peak, the programme loudness and the loudness range (loudness range, LRA).

The measurement is performed using loudness meters, which rely on algorithms for loudness and peak level measurement, based on ITU-R BS.1770-3.

With the introduction of Loudness sound measurement, programmes can no longer be delivered mixed to PPMs. The only exception is the inclusion of audio that will be processed to R.128 later in the chain or production (archive sound for example), but that is at the broadcaster´s discretion. 

The True Peak Level (specified in dbTP) represents a measure of the 4x oversampled audio to generate a true-peak value of the audio signal. This approach replaces the peaks of PPMs which were typically slow and could therefore introduce errors in the measurement of audio peaks.  The use of sample-accurate measurement helps to prevent distortion to the sound track by allowing the audio engineer to mix to a set level accurately. R.128 suggests a maximum true peak level for TV programmes of  -1 dbTP for PCM sound during production. The BBC and DPP recommend a true peak of -3dBTP for audio that will be encoded for delivery to the home (eg Dolby E, Dolby Digital).  The mix must be below -3dbTP if it is to be broadcast, and cannot exceed it. 

It is advisable to use a true peak limiter for monitoring sound.

The program loudness (specified in LUFS) is a measure of how our ears and brains perceive the loudness of an audio signal. The programme loudness (Loudness Programme or Integrated Loudness) is measured over the entire program length, whether 30 seconds TV commercials or 90 minutes feature films. For delivery of finished programmes, the programme loudness has to be -23 LUFS (±0.5LUFS), this value is also referred to as the "loudness target". Some R.128 meters  don’t display the actual figure, e.g. -23LUFS, but instead display the difference – so a correct delivery would be 0 LUFS on one of these meters, and upward deviations would be recorded as positive (e.g. +2LUFS), downward deviations displayed as negative numbers (e.g. -2LUFS).

The loudness target value of -23.0 LUFS must be hit with a maximum deviation of ± 0,5 - 1 LUFS depending on the broadcaster delivery requirements. This value is especially true for live productions, with post produced productions having a target value of +/- 0.5 LUFS. The maximum measurement tolerance for a loudness meter, according to EBU Tech 3343, is ± 0.1 LU. See EBU Tech 3343 (externalPDF).

Loudness uses a gating process to ignore sounds that are below -70LU. This means that the integrated programme sound is addressing programme sound not silence or faint background sounds. See EBU Tech 3341 (externalPDF).


DK1 Loudnessmeter


Loudness meters also display Momentary Loudness (M integrated over 400 ms) and Short-term loudness (S, intergrated over 3 seconds). Some broadcasters who commission promos and commercials also specify maximum Momentary and Short-term loudness values in addition to the program loudness. During a live performance, the Momentary Loudness is an important indicator of the loudness development of the programme.)

Loudness Range (LRA) in LU describes the loudness scope of the programme. Heavily compressed material, such as old TV programmes and films  or commercials, generates an LRA 2-5 LU, while current production of sports, music and movies typically reach 8-20 LU. Although the LRA is similar to production  audio dynamics, it is a statistically determined value, which describes the dynamics of a program segment over time. The maximum LRA has now been set by many broadcasters to 15 LU for stereo and surround, the measurement accuracy of the LRA display is ± 1.0 LU - EBU Tech 3344 (externalPDF).

In live broadcasts, it’s important to monitor momentary loudness and short-term loudness. The engineer now monitors more than just the peak – they now look across the actual program loudness as a whole. Numerous manufacturers - from DK-Audio, Dolby and RTW to TC Electronic - offer standardised and practical solutions. In extremely dynamic material such as football broadcasts, a carefully adjusted loudness Leveller in the signal path is recommended.


[Figure: Typical targets for the modulation by EBU R.128]


1 LU (Loudness Unit) and 1 LUFS (Loudness Unit Referenced to Full Scale) correspond to the scaling exactly 1 dB



In post production, many broadcasters and studios rely on automated loudness normalisation using products from Minnetonka Audio, Nugen and others. The finished file will be analysed by this software and automatically adjusted to the target values for True Peak, Program Loudness and Loudness Range. It’s important to carefully check the audio delivery requirements of the broadcaster, as some specify momentary and short term loudness levels.

ITU-R BS.1770 "Algorithms to measure audio programme loudness and true-peak audio level" (external link)

Author: Karl M. Slavik, Arte Cast Vienna

Related Articles: