8 TVBEurope


News Guest Opinion


www.tvbeurope.com August 2013


One of the biggest challenges is anticipating if an incoming programme is already compliant


Loudness compliance: closer to artistic intent


By Craig Todd, senior vice president and chief technology officer at Dolby Laboratories, and SMPTE Fellow


THE STANDARDS and recommendations governing loudness have been refined over more than a decade of work, and loudness measurement and compliance has now matured into young adulthood. Nevertheless, differing approaches to loudness management — and their impact on content quality and artistic intent — do continue to cause tension across the broadcast industry. One of these issues, the


overprocessing of audio, stems from fear of being non- compliant with loudness specifications that, in some countries, are the subject of government regulations. When broadcasters first faced the challenge of meeting loudness regulations, most did so with relatively little education on the subject of loudness and with only a small selection of loudness correction solutions available on the market.


One of the biggest challenges


Craig Todd: Processing content with a single-ended realtime processor can wreak havoc on artistic intent, sucking the life out of a programme


Understanding that penalties


could follow if even a very small percentage of aired content were found to be noncompliant, broadcasters embraced the no- fail approach of dropping a realtime signal processor, such as a limiter and compressor, into the signal path. In this way, they could ensure that the output always remained compliant, with the -23 LUFS set by EBU R 128 or the -24 LKFS set by the ITU- R and the ATSC.


for broadcasters is anticipating if an incoming programme is already compliant — i.e. whether or not it was created properly or subsequently measured and adjusted to meet appropriate specifications. Consequently, it became common for broadcasters to employ a signal processor for any signal they couldn’t ‘trust’ and to output everything as specified by the EBU. As initially no programmes were trusted, all programmes suffered from processing. Processing content with a single-ended realtime processor can wreak havoc on artistic intent, sucking the life out of a programme — and the effect is multiplied if audio is passed blindly through a cascade of realtime processing devices used by the content producer, broadcaster, cable operator, and in-home receiver. The same programme output by different stations can sound very different — from very good to very bad — depending on the processing applied. While reliance on clearly defined media delivery


parameters and the use of automated file-based QC on incoming content have begun to mitigate this problem, an overabundance of signal processors remains, and the consumer’s experience of audio continues to be compromised. One possible solution to this issue is to include a set of loudness metadata in the audio bitstream to indicate details such as loudness measurements, correction type, compliance type, speech flags, and PGM boundary information. With a framework for processing this data, future file-based analysis and correction tools would be able to adapt dynamically in their treatment of content, thereby eliminating unnecessary realtime processing that might undermine audio quality.


A focus on loudness Preservation of artistic intent benefits from getting content right from the very beginning. Among other things, this means that, further up the chain, content producers must consistently mix to the required loudness, as is suggested by both


the EBU and ATSC, and to a reasonable dynamic range. As an increasing number of countries across Europe legislate normalisation of audio according to EBU R 128, there remains some debate as to how best to address the loudness recommendation within the production environment. Differences in how loudness


measurement is implemented do pose challenges in international programme delivery, as certain types of content wind up being processed to very different effect. Though the EBU -23 LUFS target level differs from the -24 LKFS recommended by both the ITU-R and the United States’ ATSC (by one decibel and one letter in the designator), for most programming the result is very similar. Other variables, such as dynamic range and true peak levels, do also influence the end result — but more significant is the fact that North American countries have focused on keeping the loudness of dialogue consistent, and European countries following the EBU specification have focused on overall loudness. In wide dynamic range content such as action movies or some music programmes, which have major fluctuations, loudness measurements can be very different depending on whether dialogue or overall average level is measured. Because the average level measures higher than the dialogue in these programmes, European broadcasters tend to either bring the whole average down, (leading to dialogue being quieter than commercials for the wider dynamic range programmes) or to reduce the dynamic range by use of single ended compression. While such signal processing undermines artistic intent of those moviemakers that provide wide dynamic range, it appears that different markets are content to make do with that loss in order to avoid occasional discomfort with the loud sections of movie soundtracks. Ideally, loudness measurement and correction ensures the consistency of loudness across programmes, promos, and commercial content while making the least possible impact on the characteristics of the audio signal for programme content. The industry continues to work its way toward this ideal, and its ongoing maturation will, in the end, bring consumers the superior quality of experience intended by loudness standards and regulation.


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