We explore digital wireless tech by learning about what modern RF experts think of the trend towards more digital systems and the potential benefits.
Over recent years, we’ve seen the RF landscape change dramatically. Our industry, in particular, was significantly affected, with PMSE users (Programme Making and Special Events) losing access to large portions of UHF spectrum since the initial adjustments in 2012.
Ongoing changes came thick and fast, with the latest arriving on October 17th 2016 when Ofcom confirmed their intention to clear the 700MHz band by May 2020. Once completed, this next clearance phase will leave PMSE users squeezed into the remaining UHF bands (470-694MHz). With clean spectrum becoming increasingly premium, and the demand for new wireless devices growing daily, it’s safe to say, things are about to get crowded!
As congestion grows and space continues to shrink, modern RF engineers are turning increasingly to digital wireless technology as part of the solution. To help understand why, we spoke to some of the industries leading RF experts and sound engineers. First up was Steve Caldwell of Norwest Productions, who we managed to catch upon returning from a summer spent coordinating RF at the Rio Olympic and Paralympic games.
Caldwell sees huge gains with digital wireless tech, particularly when considering spectral efficiency. “One of the distinct advantages of using wireless microphones that utilize a digital transmission scheme is the enormous amount of channels that can be packed into a minimal amount of spectrum,” he states with enthusiasm. “As the nature of digital transmission allows contiguous alignment of channels, with no interstitial spacing required, radio microphones can literally be ‘packed together’. Of course, some spectrum management is still required, but it is still a huge advantage over traditional analogue systems.”
While digital systems clearly enable significant gains in spectral efficiency that can benefit large-scale events in congested RF environments (such as Olympic games), Caldwell sees the majority of adoption on a smaller scale, at least for now. “By far the biggest adoption of digital wireless I have seen in the past few years is that of the semi-pro, and pro-sumer community. The ease of use and reliability that the digital wireless systems have brought to the average user is a huge step forward.”
“At Norwest, we’re also seeing a huge move to digital in the corporate AV space,” he continues. “We replaced all of our analogue UHF systems with digital UHF systems, for these kind of gigs. The ability to set them up with a minimal amount of spectrum management has improved the efficiency tenfold.”
Caldwell’s comments on the huge benefit of digital systems for corporate AV applications were echoed by Blitz Project Manager, Peter Russell, who comments having recently deployed a number comprehensive digital wireless systems at major conference events across Europe.
“Being able to reliably operate a large number of channels on a narrow range of frequencies is very important to us and our clients,” he explains. For example, we are the in-house AV supplier for ExCel in Docklands, who are now regularly doing shows that require over a hundred channels. We need technology that allows us to cope with those client demands, often without pre-production or the opportunity to visit a venue or assess its suitability beforehand. Our wireless hardware has to allow us to reliably operate the maximum number of channels, no matter how RF-heavy the surroundings might be or how helpful the local RF regulatory framework is.”
Russell continued, giving particular credit to the ability of some digital wireless systems to operate in the ultra-efficient high-density mode, which comes into its own within his line of work. “In Milan a couple of years ago I was setting up wireless mics for a client’s keynote speech. I only needed 12 channels or so, but I only had one working frequency — normally I would expect to have 50 or so. Turning up and finding you’ve got that kind of problem is never fun, but it happens more and more. In this particular case, the venue was about half a kilometre from the local TV station, and also, the stage we were working on faced directly towards the TV station transmitter, which meant there wasn’t even any damping effect from the building. Almost every frequency was in use, and we could only find space to work at the extreme end-stops of the band. Cases like that are where a high-density mode is useful: you can squeeze more channels into the remaining gaps.”
Analogue vs. Digital
One debate that always rears its ugly head concerning the influx of digital wireless systems is the age-old analogue vs. digital audio question. A large segment of the audio industry still has a strong partiality toward analogue equipment for tonal aesthetic reasons —leaving many feeling ambivalent about digital wireless. With analogue vs digital wireless, the debate takes on a whole new meaning, as the main difference between analogue and digital is how we modulate the RF carrier. At a recent digital wireless open day, Shure UK Area Sales Manager, Dave Phillips shed some light on this age-old debate.
“The chief purpose of a wireless system is to replace a cable. In doing so, it should sound as good as a cable and be as reliable — if not more so. Analogue systems sound great in good RF conditions, but they’re inherently noisy, and the audio suffers when things get tough. Properly engineered digital systems offer clear and crisp audio even under difficult circumstances.”
From an audio perspective, Phillips goes on to highlight how modern signal chains — combined with strong RF performance — might influence the debate. “Most Productions already have digital desks, and increasingly, the signal path between stage and the amps is entirely in the digital domain. In good RF conditions, it’s hard to differentiate between an analogue and digital wireless system from the FOH position, but when the noise floor is high, a digital system will come out on top.”
The sound quality of digital wireless systems hasn’t gone unnoticed by Sound Engineer, Tour and Production Manager, Mark Portlock, who was quick to sing their praises after a recent tour.
“Throughout this year, I was fortunate to start as Tour Manager and Sound Supervisor for new London Brat Pop act, GIRLI. During the summer, I tested a few digital systems for GIRLI at a mixture of small club shows and festivals; I was immediately impressed by the sound quality. Since then, I’ve deployed the systems on a support tour with UK artist Oscar. We used in-house engineers for the shows and on every occasion they commented on the great sound quality.”
Portlock also expressed great appreciation for the solid RF performance of digital systems. “Being the type of engineer that likes to place the main emphasis on how music feels rather than technical details, I’m a big fan of reliability made simple.”
The case for spectral efficiency is evident; spectrum is a scarce resource, and digital systems go a long way toward providing practical solutions to some of this problem. And, it’s clear the audio quality has the potential to better analogue systems in many cases. But for every force, there is a counter force — for every action a reaction. In the case of digital wireless, this repercussion comes in the form of latency, as Tuomo Tolonen, Shure UK Pro Audio Manager explains:
“Latency is a subject that comes up regularly when discussing digital wireless systems, and rightfully so — it’s an important factor. Every conversion from analogue to digital or back to analogue results in latency. How much latency is acceptable really comes down to the application. Also, we shouldn’t just focus on the latency of a radio mic itself as the more important figure is the overall accumulative latency of an entire system from mic to speaker. If it’s a live performance for instance with an artist on IEM’s, it’s likely you would aim to have the latency figure as low as possible. A corporate event, on the other hand, can probably live with a slightly larger number. That said, Shure ULXD has a latency of 2.9ms so it’s already very low and would work fine in either situation.”
The Bottom Line
There are many advantages to digital wireless systems, some of which are beyond the scope of this article. There’s the inherent advantage of signal encryption, for example, which is perfect for information-sensitive events. Also, there’s the increased networkability, with remote software control and monitoring. However, what really stands out time and time again, is spectral efficiency. The fact remains, clean spectrum available for use by wireless microphones is shrinking while the demand for ever greater channel counts is on the increase. From the comments received by our contributors, it’s clear to see that digital wireless technology has now advanced to a point where, so long as we consider latency carefully, the advantages now considerably outweigh the familiar disadvantages.