Wireless microphones: Shifting bands

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There is no doubt that wireless microphones offer significant advantages to the AV world. But the cloud over available RF spectrum is casting a shadow far and wide. Paul Milligan reports.

A quick look at consumer technology reveals that a wireless option is preferred to a wired one. Just recently, as Apple did away with the 3.5mm jack on its iPhones, the market has seen a rise in the demand for Bluetooth earphones and headsets. But does the preference for wireless options prevail in the professional AV industry when it comes to microphones?

There is no doubt that wireless microphones come with significant advantages. During a live performance or important presentation the last thing you want to worry about is tripping over a long wire. But as we have seen with other technologies that have moved from wired to wireless, it’s possible you’ll encounter some teething problems along the way. When you add the ongoing confusion regarding the RF spectrum and wireless microphones, where the only certainty is uncertainty, you may ask yourself why bother?

When you talk about any wireless technology inevitably you have to talk about interference, and with microphones it can be a critical issue. Daniel Ku, senior applications manager for Mipro, succinctly says: “Interference in the RF spectrum is an inevitable phenomenon.” As the technology is evolving does this mean interference is becoming less of an issue?

Sadly, the outlook is downcast. Tobias von Allwörden, senior product manager, professional audio for Sennheiser, says: “RF interference is still the number one issue, and the problem is getting bigger. The available spectrum is decreasing, leaving you with less room to manoeuvre.”

This sentiment is backed by another leading name in wireless microphones, manufacturer Shure. Stuart Stephens, senior specialist, product manager, pro audio and retail, comments: “The threat of interference is arguably higher today and in the years ahead than ever before. We are seeing a continuous loss of UHF spectrum to the mobile sector. Since 2012 our industry has lost nearly 50% of usable UHF spectrum.”

Andy Fong, senior manager for product marketing at Shure Asia, adds: “Interference is unpredictable. Nowadays, most of the wireless systems are equipped with a scan feature for users to setup the wireless microphones without interference. We always recommend customers scan the RF environment before assigning any frequency to receivers and transmitters. However, the scan environment may be completely different during the setup period and actual live performance.”

Fong details how Shure products are built to be resistant to interference and says: “Shure wireless systems have a capability to find clear frequencies based on the actual RF scan result, some of the product series are even able to detect interference (i.e. ULX-D and Axient Digital Wireless Systems). However, detecting interference may not be the ultimate solution when dealing with interference. In Axient Digital, the wireless systems can also avoid interference by automatically switching to another clear frequency of receivers and transmitters. It can completely avoid interference during important events like an artist performance or a CEO presentation.”

There are other factors that can cause interference and these need to be accounted for says von Allwörden: “Sources can be LED walls which are quite omnipresent in today’s entertainment industry, and other lighting equipment and controls. They all emit spurious radiation in the UHF spectrum.” Luckily, a few manufacturers of videowalls have become aware of this and are trying to remedy it.

Interference is becoming increasingly tricky to pinpoint says Ian Bridgewater, director at TOA Corporation UK: “It is quite difficult for some users to recognise other entities that would interfere with it, things like radio transmission towers, or (defence) sites that have ground radar.”

There have been many articles written in the professional AV press about the RF spectrum over the past five years, so without going over old ground where are we at right now? Stephens says: “UHF spectrum continues to shrink at alarming levels. The UK is due to clear the so- called 700MHz (703MHz to 790MHz) band by 2020 leaving users with nearly 50% less usable spectrum than we had in 2012.”

Things are no different in Asia as Fong from Shure Asia details: “In recent years, we have been experiencing lots of wireless frequency reallocation for wireless microphone systems in Southeast Asian countries including Singapore, Malaysia, Indonesia, the Philippines, Thailand and Vietnam. The new spectrum assigned for wireless microphones are commonly shifted to below 700MHz. The spectrum above 700MHz was sold or auctioned for telecommunication services similar to what happened in the United States or some European countries.”

Microphone manufacturers and their partners seem to be in no position to bargain with regards to wireless frequency shifts. Fong from Shure Asia says the best course of action is to roll with the changes: “From the standpoint of a manufacturer, we have to produce products in a new frequency range so as to comply with the new regulations as quickly as possible. Thus, we need to have all wireless systems operating in the new frequency fulfilling the new regulatory requirements of the industry. Our channel partners also need to help educate the market about the changes of wireless microphone usage. We have found that quite a lot of end customers do not have much knowledge or experience of the regulations and requirements of wireless microphone usage. From a customer perspective, it is a good opportunity to update the wireless systems with latest technology. Most importantly, the end users can gain more knowledge about the legal frequency range and requirements of wireless microphone usage in their countries. They can use the wireless microphone system without violating their country’s law.”

Uncertainty, seems to be the one constant when it comes to the RF spectrum and its future. According to von Allwörden: “It sometimes feels like looking into a big crystal ball. And as there is no worldwide harmonisation, the usable spectrum also differs country to country.”

Stephens says: “The future of UHF continues to be uncertain as the relentless push from mobile service providers seems to have no end. It’s clear that mobile technology is part of our day-to-day lives and that sufficient bandwidth must be available to cater for demand. The irony of course is that the very same spectrum that is being made available to deliver content is the same spectrum that is being used to make content in the first place and we are at serious risk of diminishing the production quality that our market is recognised for.”

The future isn’t looking rosy agrees Alex Lepges, marketing director for EMEA at Audio-Technica, but he isn’t completely without hope either: “With the growing demand for wireless content delivery (streaming video etc.) it is certain we will see more of the spectrum disappearing for the usage of wireless microphones in the decades to come. On the other hand other spectrum currently unused by wireless microphones might become available and there are several research studies ongoing to determine which frequency ranges could be allocated to PMSE (program making and special events).”

We spoke to an array of microphone manufacturers and it seems they are all keen to work together to continue the fight for more spectrum allocation. Lepges adds: “At the end of the day it is a lobby decision and we have to make certain the decision maker understands why we need spectrum for broadcast, major sports events, theatre and musical production, live music events and other applications.”

In the meantime, Fong from Shure Asia says: “There are no easy steps to minimise the impact of wireless frequency changes on manufacturers. The development of a new frequency band always consists of a series of development processes and internal tests, ensuring that the new band can comply with the new regulatory requirement in each country. It can be easier to prepare a new frequency band for digital wireless systems since there are no hardware changes involved. While for analogue wireless systems, it may take a longer time or more resources since new components and hardware are usually required. In summary, it is a long process to create a new frequency band for countries with spectrum reallocation for wireless microphone system.”

Another issue with wireless microphones is latency. How much can you limit the delay? Is this still a significant issue or has progress been made in this regard? Lepges says: “Latency becomes an issue as soon as you want to monitor the picked up audio signal in real time. Especially when you use in-ear solutions (earphones) a total latency of maximum 10ms seems to be the limit while some more critical users define 5ms as the total maximum. With typical latencies for digital wireless mics around 3ms to start the signal chain you can see that there is not much room left for further latency from audio processing at the mixing console and a potential digital return channel.”

Stephens says: “When it comes to latency, it is important not to get too wrapped up in a single component of the system and miss the bigger picture. It is the latency of the entire audio chain that is critical. Once latency exceeds 5ms, it can be a problem when using wireless in-ear monitors, as the monitor signal arrives out of phase with the vibrations they’re hearing through bone conduction and can cause comb-filtering.”

Fong from Shure Asia adds: “When digital audio equipment getting more and more popular, audio latency will become audible by summing up the latency of each audio equipment. People are particularly concerned about the latency when they use digital wireless microphones. However, the latency in digital wireless microphone transmission is inevitable since there is error correction on digital devices during transmission. To tackle this issue, Shure has developed digital wireless systems with ultra-low latency (i.e. 2.9ms for QLX-D and ULX-D, 2ms for Axient Digital) to minimise the impact of latency on the overall audio chain.” Working in a venue with poor RF provision can be undeniably tricky, but are things improving in the ways we can correct or control audio dropouts?

Taking time to correctly set up is the key to it all was the unanimous answer and Bridgewater says: “Minimising dropout is really down to good installation and using the correct equipment, cable type and aerials.” Lepges says: “There are techniques that we use to do forward-error- correction that will help to push out the ‘edge’ a bit to signal levels but the bigger impact will always come from the operator of the wireless system. Placement of antennas, short antenna cable runs, good components and a smart RF gain planning next to frequency coordination is still the most important ingredient for a successful show.”

To this end, Shure has a Timeline function as part of its Wireless Workbench software which allows an RF coordinator to perform a walk test around the venue while it records live audio and RF data, whereas Sennheiser’s Digital 600 Series has in-built error correction able to repair ‘a few ms’ of lost signal without a noticeable audio dropout.

The move from wired to wireless will happen in the microphone world, we know it will because it has happened to every other kind of electronic technology. Wireless is the default because it is handy, versatile and flexible. What is holding up the move to wireless is the fight for RF spectrum, which sadly, seems to have no end in sight, and is something we were saying at this same point five years too.

Efforts at continual improvement are important as Rijsbrack believes there is room for growth down the road. He says: “Asia still has a lot of capacity. There are many opportunities for growth via new builds as they are far from reaching the saturation point compared to other regions. Smaller cities offer the best opportunities, and with affordable boothless projection cinema now a reality, smaller exhibitors have a better business case for cinema.”