Sound advice: spectrum squeeze

May 2020 is the deadline for pro audio, AV and production users to clear out of the 700MHz band to make way for the next wave of mobile data and communications operators. Phil Ward investigates.

As soon as the TV broadcasters finally switched over to digital, vacating the old RF bandwidth that we all knew and loved from Watch With Mother onwards, new interests began to fill the vacuum: 790mHz to 862mHz was occupied by 4G in 2012. Just over a year ago, UK regulator Ofcom announced that May 2020 was the deadline for professional audio, AV and production users to clear out of the 700MHz band in order to make way for the next wave of mobile data and communications operators. The squeeze was on again.

In less than 10 years, nearly half the usable spectrum that we all used has been either taken by, or earmarked for, other parties. Latterly another drain on resources hoved into view, even before a single grain of dust had settled: White Space Devices have made their own claim on UHF frequencies as the Internet of Things progresses and its online wireless facilities take over our lives. Pro AV, however essential, just keeps getting elbowed out of the way.

It was called the Digital Dividend Review, but the surplus has not fallen evenly. The first pragmatic solution adopted by the pro audio market leaders was to move wireless microphone use from Channel 69 to Channel 38, and a sustained campaign by industry lobbies saw this through without too much pain. But making the 700mHz band available to the same vested interests in mobile communication only makes matters worse – even for digital television, which will have to be repacked at lower frequencies from 470mHz to 694mHz.

Notwithstanding this impact, most inside observers agree that the latest phase of encroachment is more insidious and less generally understood by professionals and public alike. The switch to digital TV was easily grasped as a concept, but clearing bandwidth for the abstruse appetites of the ‘app’ is less tangible, and therefore less easy for the lobbies to address.

What we do know is that 694mHz to 790mHz will be cleared in the UK by May 2020. Ofcom defines three tiers of access to the remaining spectrum: Digital Terrestrial Television (DTT); Programme Making & Special Events (PMSE), which is the category under which all production technology including wireless microphones, in-ear monitors and wireless AV falls; and White Space Devices. Each user must be licensed, and the licensing process is, to say the least, complex. In one sense, placing PMSE in the midst of these interests – never mind the mobile giants – already compromises bandwidth quality.

But once DTT begins to occupy frequencies below 694mHz – it’s already started – PMSE devices will have an even harder job of maintaining efficiency. The best thing you can do at this stage is to keep regular tabs on the changes as they happen in all of the regions that might affect your business, local or national. Find out which frequencies are available and what the plans are concerning Ofcom’s management of that spectrum, especially if the equipment you rely on operates on or below the 700mHz band – Ofcom does provide a 700mHz ‘look-up tool’ on the web site (www.ofcom.org.uk). There are compensation packages, too, for those users genuinely affected by the developments – so look into these as well.

Examining the cloud for some silver lining, meanwhile, we can acknowledge that the squeeze on spectrum has at least hastened the development of much better digital wireless systems of various types. This is mostly because digital systems enable you to fit more discrete channels than analogue into the same area of spectrum, making good use of their accuracy and avoiding the cumbersome navigation technique used by analogue systems known as Frequency Modulation – basically, this is a technique that needs a lot more space to work out the best path through the air.

While some manufacturers still worry about issues of sound quality and latency that stick doggedly to the digital paradigm, the market leaders have moved on to accept the post-squeeze landscape as a post-analogue landscape. Shure has provided a new generation via QLX-D, ULX-D and Axient Digital, while Sennheiser’s Digital 6000 follows the Digital 9000 system into a wider range of applications on a wider range of budgets – including the everyday needs of corporate AV as well as what might be considered as the élite preserves of stage performance.

Shure’s claim is that each megaHertz of frequency passing through the Axient Digital system can accommodate over three times the channels managed by the original analogue Axient wireless system, a figure doubled by switching to High Density mode.

Faced with these statistics, spectrum users are going to find that any other concerns will stack up next to the pile of unanswered questions laid down by UK voters who wished to remain in the EU. We are Brexiting 700MHz, and that’s that: you can do it the hard way or the soft way, but the latter will have to be digital.

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