Audio monitoring: critical to visual media services


Simen Frostad TV-Bay Magazine
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by Simen Frostad
Issue 89 - May 2014

Its 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, thats 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 its 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 channels 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 theres an lot of audio monitoring going on under the hood. This is because audio monitoring has become extremely demanding, 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, its a serious failure even if just one of those 5.1 or 7.1 components disappears.

Add to this the load involved in multiple-language services, where there might be five 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.

As always when a lot of services need monitoring, the design of the monitoring technology is critical to efficient 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 benefits 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 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.

H265/HEVC may change this over the next twelve months or so. The video part of the specification 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 specification.

Whatever the outcome of this process over the next years, theres 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 efficiently, as part of the overall monitoring environment.


Tags: iss089 | bridge technologies | audio monitoring | Simen Frostad
Contributing Author Simen Frostad

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