TV-BAY Magazine

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In the post-production environment, loudness metering software (plug-in or application) can offer a considerable advantage over a stand-alone, real- time hardware meter because it can not only measure a program in its entirety, but it can do it faster than real time. The main target measure of integrated program loudness requires that the loudness be measured over the entire length of the program. For example, making a 30-second edit in a 50-minute documentary will require the entire 50 minutes to be measured again — something of a time issue when using real-time hardware meters. Many nonlinear editors (e.g., Avid Pro Tools® and Media Composer®) allow for faster-than-real-time analysis, and there are also offline file-based tools that can speed up the analysis considerably, avoiding large amounts of unwanted downtime while acquiring measurements. Unlike hardware meters, loudness metering software allows you to get the most out of your nonlinear editor. True-Peak Limiters Unlike sample peak limiters, a true- peak limiter can handle the intersample true-peak requirement inherent in all of today’s standards. Loudness normalization deals with loudness jumps and consumer satisfaction issues, but you still need to measure peak levels to avoid distortion in the signal. True-peak level is a measurement of the intersample peak. Maximum peak measurement is specified in order to avoid noticeable clipping and distortion, but because of the way audio is sampled, the real audio level might have gone above the maximum peak level between samples. True-peak level is designed to measure that real level and avoid clipping. It can be tempting to use sample peak limiters to do the job, but in reality there are no “safe” settings for a sample peak limiter. A sample peak reading can often read as much as 6 dB higher on a true-peak meter, and it is not possible to set a traditional brick-wall limiter (very high ratio and fast attack times) to be safe enough. While you can artificially set limits using PPM, this approach simply introduces another layer of complicationIn reality, the only way to be sure of correct true-peak values is to use a true-peak limiter. Offline Correction Once a mix is more or less loudness- compliant, offline tools can speed up the last part of the normalization process. These tools can be used within the editing environment to bring a mix into line quickly, correcting any true-peak overshoots as it goes. Batch Analysis Most busy post-production environments will benefit from some form of automated loudness processing. Acting as a rapid fail- safe system and internal QA, a batch processor can automatically assess files for compliance and correct or reject as necessary. Unresolved issues Because international recommendations are all based upon the same ITU standard, most of us in the industry agree about how to approach loudness control. There are, however, issues that have yet to be resolved, most notably the difference between a 5.1 mix and its corresponding downmix. It is common for the downmix to differ slightly in loudness from the 5.1 mix, but what makes the issue 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 jump in loudness depending upon the configuration. Reaching for a magic metadata bullet would be one solution, but that solution assumes the metadata is accurate and the appropriate device is capable of reading and responding properly. ASK OUR EXPERTS Resolving problems with dialog clarity is the next most pressing issue. After loudness jumps, dialog intelligibility above the background audio is the thing consumers complain about most. Whilst it is possible to measure loudness differentials, there is little published research in this area. Even so, it is fairly simple to devise internal guidelines to check for potential problems. Another potential pitfall related to dialog clarity occurs when reducing the dynamic range in film in order to repurpose it for television broadcast. Traditional compression techniques do not take into account the level of the dialog in the original mix, and clarity can suffer as a consequence. Normalizing loudness in either of these situations involves creative decisions that are best applied by the post-production engineer in the context of overall loudness compliance. What’s the future for loudness? If fewer complaints are any indication, loudness normalization has been a boon for consumers. Now that we have a solid foundation for loudness control, it’s time to dig deeper and refine our solutions. As the loudness market matures, new techniques and considerations are emerging. The aim is for loudness to be a primary consideration during production. As tools improve, we’ll use loudness parameters and transferable, objective measures to check whether audio is not only compliant, but also target- appropriate. Audio engineers will use these same tools to produce programming that better satisfies the myriad different creative and consumer demands. POST YOUR QUESTION ONLINE: Search ‘tvbay’ Tel. +44 (0)1635 237 237 Email. TV-BAY MAGAZINE: ISSUE 77 MAY 2013 | 49 TV-BAY077MAY13.indd 49 02/05/2013 21:18