TV-Bay magazine

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AUDIO Audio monitoring is critical to visual media services by Simen Frostad, Bridge Technologies I t’s a fact of TV broadcasting that audiences will tolerate reduced visual quality much more readily than any impairment to the audio. So long as the audio continues and is intelligible, viewers tend to put up with glitches in the video or even temporary loss of picture. But if a broadcaster lets the audio quality drop or loses audio altogether, that’s when the viewer gives up and switches channel. So audio quality is critical to TV and video media services. And if audio monitoring seems to lurk in the shadows in the context of digital media services, while the monitoring of video occupies the spotlight, it is perhaps because audio is such a vital part of the service that it is unquestioned. The nature of human perception also has something to do with this. An operator can sit at a monitoring console and comfortably eyeball 50 services or more concurrently, with a well-designed display. But it’s quite impossible for anyone to monitor more than one audio source at the same time. So the audio monitoring has to be done robotically in the background, and only when error conditions arise does a visual alert make its presence felt. In a system like the Bridge Technologies VB288, the immediate impression is of video monitoring activity because the content extraction processes continually display each channel’s video stream. The audio monitoring is happening too, but without a visual presence on the display – until a service degradation or failure occurs. In fact there’s an lot of audio monitoring going on under the hood. This is because audio monitoring has become extremely demanding, 68 | TV-BAY MAGAZINE: ISSUE 89 MAY 2014 with loudness compliance required by law, and with widespread use of surround sound audio. Monitoring systems like the VB288 have to continuously decode the audio to check for loudness compliance, and for the presence of all the components of a surround sound source. For the service provider, it’s a serious failure even if just one of those 5.1 or 7.1 components disappears. disappear. Unlike the video component of a service, the audio component has hitherto been delivered at one quality level only. While H264 adaptive streaming to mobile devices ‘downshifts’ the video quality when receiving conditions mean that the bandwidth is inadequate to view the better quality without buffering, the audio continues to be streamed without this adaptation. Add to this the load involved in multiple-language services, where there might be fi ve language sources for a channel, each with 5.1 sound (making 30 channels to check), and the audio monitoring requirement for a visual media service becomes very demanding. H265/HEVC may change this over the next twelve months or so. The video part of the specifi cation is pretty settled, but there are still different directions on the audio. So while H265 compliant monitoring systems will have to support all the codecs in the same box (MPEG-1, MPEG-2, AAC, HE-AAC and beyond), there may also be provision for multi-versioning adaptive audio in the specifi cation. As always when a lot of services need monitoring, the design of the monitoring technology is critical to effi cient operation. If the monitoring information is presented clearly in a way that allows a small number of operators to keep on top of a large number of services, this benefi ts the service provider not only in terms of cost but in higher service quality too: when operators instantly get the information they need, repair times are dramatically shortened. One big difference between audio and video delivery may be about to Whatever the outcome of this process over the next years, there’s the prospect of greater diversity in audio delivery, and therefore in audio monitoring. Digital media service providers will need to keep abreast of these developments, and build monitoring systems that handle the audio monitoring requirement elegantly and effi ciently, as part of the overall monitoring environment.