Loudness measurement: One year on


Jonathan Schorah TV-Bay Magazine
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By Jon Schorah, creative director, NUGEN Audio.

With, much of Europe and the U.S. now producing broadcast audio to meet loudness standards, Jon Schorah, creative director of NUGEN Audio, reflects upon the current state of play, the lessons learned along the way, and what’s to come.
Playout or Production Normalisation?
Commonly there are two ways to achieve integrated program loudness standards. One is playout processing, which is a catch-all approach to compliance. The alternative is to pre-process the material to ensure it is normalised before playout, or better still meet standards during production.
While playout processing is indeed commonplace and delivers a technically compliant broadcast, there are drawbacks. In extreme situations, a particularly loud commercial that has been brought into line with real-time processing can even generate a loudness problem if the program material that follows is itself relatively soft. A both-and solution commonly adopted is to bypass processing with compliant material and switching processing on when material is non-compliant or of unknown provenance.
Ultimately, the best audio quality is achieved by producing audio to loudness specification during production/post production. Whilst automated systems are good at aligning and correcting for small inconsistencies, creative decisions are best left to the creative professional. So while the situation is already considerably improved, there is still work to be done as loudness considerations move up the delivery chain.
Evolution of Loudness Standards
The recent introduction of ITU-R B.S.1770-3 reflects the continuing trend toward more detailed specification of loudness measurement.
We have seen several updates in an ongoing attempt to harmonize international recommendations and yield a truly international and universal measure. One example is the adoption of a relative gate in ATSC/A85, and the corresponding revision in EBU R128 from the G8 gate to the G10 gate, bringing the two into alignment.
Despite these efforts, there are still areas of intense discussion, especially over whether or not to use the dialog anchor. Putting the politics of the debate aside, it’s easy to see that each method has its advantages -- both in terms of simplicity and consistency of results -- and you don’t have to look hard to find program material that supports one position or the other.
Increased Consideration of Other Parameters
As program loudness becomes compliant with standards, the loudness jumps that caused so many consumer complaints have largely been eliminated. As a result, attention is turning to other loudness parameters to see how they can be applied to improve audio quality even further. Two particular areas of interest are beginning to emerge – dialog clarity and the appropriate loudness range for the listening environment.
In terms of dialog clarity, one issue of concern is the transfer of highly dynamic cinema releases to the home-listening environment, where reproduction and noise floor are often far from ideal. In this situation, it can prove very difficult for the consumer to set a comfortable dialog level that doesn’t leave other parts of the program too loud or indistinct. These cases call for some form of loudness range (LRA) reduction, and work is underway to see how this could be best indicated. One interesting measure is the difference in integrated loudness between program loudness and dialog gated loudness. A difference of more than three LU/LK can be a useful indication that processing is required.
Also beginning to gain prominence is the use of the short-term loudness or momentary loudness measures within specifications. Creative minds in the advertising industry have already discovered that insertion of a section of quiet audio gives advertisers the opportunity to push the M and S loudness while still bringing the program loudness in on spec. In order to constrain this behavior, use of Smax or Mmax is finding its way into some national standards, with over-regulation being a potential cause for concern.
Getting Into the Details
There are several issues that have yet to be agreed upon on an international level, the most obvious of these being the difference between a 5.1 mix and its corresponding downmix. It is commonplace for the downmix to differ slightly in loudness from the 5.1 mix, but what makes the issue even more confusing is that the difference can be in either direction, so a simple offset is not a viable solution. Similar situations arise with dual-language, multi-mono stereo, where a consumer’s television can produce an unexpected 3 dB loudness jump – or not – depending upon the configuration. Reaching for that metadata magic bullet would be one solution, but that solution assumes the metadata is accurate and the appropriate device is capable of reading and responding properly.

Looking Forward
Clearly, based on the reduction in complaints, loudness normalization has brought a great benefit to the consumer. Having begun to get the basics in place, a second look can yield even better solutions, ultimately leading to loudness as a primary consideration during production. As tools improve, loudness parameters will increasingly be used to check audio not only for compliance, but also for being ‘target appropriate’ using transferable, objective measures. These same tools will also be available to the audio engineer to assist in producing program material that better satisfies the myriad of differing creative and consumer demands.

Tags: iss073 | loudness measurement | ITU-R B.S.1770-3 | ATSC/A85 | G10 gate | mix | loudness normalization | Jonathan Schorah
Contributing Author Jonathan Schorah

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