Loudness Whats All The Noise About


Anyone involved in our industry can’t have failed to notice the amount of noise broadcasters, manufacturers and legislators are making about audio loudness. As topics go, this one is currently red hot.

Broadcast audio that comes with annoying loudness differences can result in complaints from viewers and, in some territories, these complaints can translate into fines. Naturally broadcasters want to offer the best quality in terms of picture and sound but they also want to avoid penalties, which is why the whole subject of loudness has become so important.

But how do you guarantee good sound quality? And how do you avoid penalties? Indeed, how do you know if something is too loud? To get to grips with this topic one first has to understand the terms and phrases that are currently being used. Therefore, here is a dummies guide to some of them, followed by a few brief suggestions on how to avoid penalties and stay within the guidelines:

CALM - this stands for the Commercial Advertisement Loudness Mitigation Act, a new law that was signed onto the US statue books by President Barack Obama in December 2010. This law makes it illegal for commercials on any given channel to broadcast at louder sound volumes than the TV programmes they accompany. These differences in volume have annoyed television viewers for years and CALM is now the official US response to viewers’ complaints. CALM requires the use of technology to ensure that commercials will be played at the same volume as the programme. The law is being enforced by the US Federal Communications Commission, which, back in December 2010, gave broadcasters a year to comply. To determine audio loudness, the FCC is using guidelines published by ATSC Recommendation A/85.

ATSC A/85 - the Advanced Television Systems Committee (ATSC) published its guidelines in a document entitled Recommended Practice A/85 “Techniques for Establishing and Maintaining Audio Loudness for Digital Television”. This recommend that the loudness of all segments must be measured according to the technique specified in ITU-R BS.1770, that the dialnorm value broadcast with each segment must match the measured loudness within +/- 2LU, and that the recommended level for the dialnorm be set at -24, but any value can be used so long as it matches the segment loudness.

ITU-R BS.1770 - this Recommendation, issued by the International Telecommunications Union, is the basis for most modern broadcast loudness measurements. BS.1770 describes an effective measurement technique that uses a specially weighted power measure known at Leq (RLB). It also specifies audio measurement algorithms for the purpose of determining subjective programme loudness, and true-peak signal level. Recently the ITU updated its original document with the publication of ITU-R BS.1770-2. This incorporates a number of improvements suggested by the EBU’s R128 Recommendation, thus harmonizing both recommendations and bringing them much closer together. This harmonization means that international loudness control should provide the same results wherever it is applied and regardless of whatever standard (ATSC, ITU, EBU) is being used.

EBU R128 – this Recommendation, published in September 2010, is the result of more than two years work by audio experts in the EBU PLOUD Group. Basically EBU R128 recommends that audio is normalized at -23 LUFS +/- 1 LU, measured with a relative gate at -8 LU. The metering approach can be used with virtually all material and to date more than 20 metering manufacturers have given their support to EBU R128 by incorporating it into their products. The standard has also been adopted by many manufacturers, such as Junger Audio, that supply audio control solutions. They are now incorporating R128 as a feature in their products.
Dialnorm – this isthe metadata parameter that controls playback gain within the Dolby® Digital (AC-3) audio compression system.

How To Stay Within The Guidelines – and Avoid A Fine!

To avoid falling foul of new Loudness laws such as CALM, broadcasters - and the production companies that supply them with content - should pay attention to their audio throughout the entire production chain. This means carefully metering audio levels at all stages during a production using one of the many meters on the market that are compliant with ATSC, ITU and EBU R128.

There is also going to be a requirement to log audio data, just in case there is a complaint from a viewer. In that situation the regulators may want to see evidence that audio has not exceeded the specified limits and logged data will be vital when it comes to proving compliance.

At the transmission end of the chain, where the audio is literally going out to the viewer, there are loudness control solutions on the market that perform automatic levelling of digital audio signals. These are especially important for satellite and cable broadcasters and re-broadcasters who may be dealing with a large amount of supplied content over which they have had no production control.

Jnger Audio’s loudness control solutions, which are all fully compliant with CALM, ITU and EBU R128 loudness recommendations, incorporate the renowned LEVEL MAGIC™algorithm that is based on a Multi-Loop dynamic range control principle. This enables slow changes (AGC), fast changes (Transient processing) and Look Ahead peak limiting to be handled simultaneously, thus offering level management with exceptionally high audio quality and without coloration, pumping, breathing, distortion or modulation effects.





Tags: junger audio | iss053 | calm | atsc | itu-r | bs1770 | bs1771 | ebu r128 | dialnorm | guidelines | level magic | N/A
Contributing Author N/A

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