New WMAS Standard Promises More-Flexible, Protected Wireless Operations

Shure, Sennheiser establish early beachheads in what could be a game-changer

The lengthy narrative around the arrival of Wireless Multichannel Audio Systems is seemingly at its end. In October, the Federal Communications Commission (FCC) conferred its bureaucratic blessing on the RF technology that allows significantly denser multiplexing of audio channels onto a single wideband RF carrier. Referred to by the only slightly less unwieldy acronym WMAS, the new standard promises an easier and more flexible wireless workflow and greater protection for other services sharing the same frequency band. It is widely considered a game-changer for managing wireless signals in a narrower, denser spectral environment in the wake of multiple spectrum reductions over the past two decades.

The approval has also opened a new front in the wireless-microphone competition, one in which two of the sector’s largest brands, Sennheiser and Shure, have quickly staked substantial claims.

Sennheiser’s Joe Ciaudelli: “With WMAS, you’re using the same RF channel and the same amount of bandwidth for [multiple mics] as for one.”

Shure Senior Director, Product Management, Nick Wood puts the arrival of WMAS into broad context: “Any change in the UHF TV bands is a really big deal given the changes that have happened over the past 20 years, most of which affected access to spectrum. This one is a great development because it changes what we can do with it, and Shure has been determined to push the envelope with spectrum efficiency. What can be done with the spectrum that we have and the WMAS regulations unlock a new innovation space for us. We want to use that to let the people who produce these events, including broadcast sports, to be able to do more with the spectrum they have that day and be able to say yes to one more wireless microphone.”

Two Competitive Fronts

Sennheiser’s flagship WMAS offering is the Spectera line, introduced at IBC in September (the technology is already an ETSI standard in Europe) and demonstrated at the Americas Spectrum Management Conference in Washington, DC, last month. It features wideband, bidirectional bodypacks and a central unit that can handle up to 32 I/O. Its bidirectional wireless ecosystem supports data and audio control in a single RF carrier for all components and for such parameters as IEM volume, audio level and settings, RF health, and battery status. Sennheiser asserts that it is able to accommodate an entire production in a single wideband (6- or 8-MHz) RF carrier.

Shure’s entry takes the form of a new iteration of the company’s Axient wireless series: Axient Digital PSM combines its first digital wireless in-ear monitoring solution with its first WMAS-enabled product. It was announced Oct. 22 (although it had been selectively previewed privately two weeks earlier during the AES/NAB expo in New York, at which Sennheiser did not exhibit). Stereo capability enables Axient Digital PSM to operate as two discrete channels, allowing a stereo audio channel to function effectively as two mono IFB channels. Additionally, the capability to send Dante signals to the Audio Digital Transmission Exchange (ADTX) simplifies routing. The WMAS wideband implementation supports up to 28 channels per 6 MHz in the U.S. and 40 channels per 8 MHz in Europe; a narrowband mode provides access to more RF output power per channel while maintaining spectral efficiency at 17 channels per 6 MHz.

Changing the Game

The new FCC rules will allow WMAS to operate in the broadcast-TV bands and in the 600 MHz duplex gap on both a licensed and an unlicensed basis and in other Part 74 LPAS (low-power auxiliary stations) frequency bands on a licensed basis. Power restrictions are 50 mW in the VHF-TV bands, 250 mW conducted power in the UHF band, 20 mW in the 600 MHz duplex gap (653-657 MHz), 250 mW conducted power in the 1435-1525 MHz band, and 1 W conducted power in all other bands, according to the FCC’s website. WMAS will enable more wireless microphones to operate in the available spectrum (more microphones per megahertz of spectrum), providing additional options when more microphones are needed.

The WMAS rules do not alter existing spectrum rights or expectations regarding spectrum access and availability related to other authorized users’ sharing the frequency bands with wireless-microphone operations (including, for example, broadcast licensees, Wi-Fi, and white-space–device users).

Sennheiser’s Take

For broadcast-sports applications, Ciaudelli — who contends that Spectera is the most innovative product the nearly 80-year-old company has ever produced — notes a broadcaster’s typical complement of one transmitter for a microphone and one receiver for an IFB. That, he says, can be condensed into a single transceiver using Spectra WMAS. There’s a similar benefit for large-scale events, such as the Olympics, in which various echelons of wireless mics are in either active or on standby status as a production unfolds.

“With WMAS,” he explains, “you could give the vast majority of the spectral resources to the mics that are currently on-air. The mics that are, let’s say, ‘on deck’ you give just enough resources to make sure that they remain linked to the base station in a ready mode. You’re using the same RF channel and the same amount of bandwidth for everything as for one.”

It could, Ciaudelli adds, make irrelevant the so-called “Super Bowl Wars,” an ad hoc event in which every wireless microphone in the stadium is turned on the Thursday before the annual NFL Championship Game to test the overall system’s robustness, resilience, and frequency coordination. “Every time you turn on a mic and put more RF power in air, you’re raising the RF noise floor,” he says. “Sennheiser’s Spectera operates at 50 mW: the power of a single wireless mic, regardless of the number of audio channels you multiplex on it. So there’s only ever 50 mW of RF power in the air. It scales linearly.”

Shure’s Take

According to Shure, the RF performance and spectral efficiency of Axient Digital PSM make it a good fit for sports applications, especially as broadcast talent moves deeper and more often onto the field and athletes are increasingly wired for two-way sound during play. In fact, some beta testing around that has already taken place. (Shure says it is unable to publicly disclose the identities of these beta users at this time.)

“We have been beta-testing Axient Digital PSM with broadcast customers during major sporting events specifically for IFB purposes,” says Shure Market-Development Manager Ben Escobedo. “The feedback has been overwhelmingly positive, particularly highlighting the improved audio quality and ease of deployment.”

Axient Digital PSM’s stereo capability allows it to operate as two discrete channels, allowing a stereo audio channel to function effectively as two mono IFB channels. Additionally, the capability to send Dante signals to the Audio Digital Transmission Exchange (ADTX) simplifies routing.

“The WMAS mode, which offers four stereo channels, is perfect for IFB use,” he adds. “It enables you to achieve eight mono IFB channels on a single frequency within an 800 kHz bandwidth.”

Consensus on Specifications

Shure’s Prakash Moorut expects the new RF format to help defend against future reductions in spectrum availability.

Some points of contention in the FCC’s rulemaking process around the technical parameters were WMAS’s output power, restrictions on bandwidth, and extension of the technology to unlicensed users. Shure, for example, lobbied for including unlicensed users. Prakash Moorut, global head of spectrum and regulatory affairs, Shure, notes that 94% of the company’s users fall into that category, according to a survey by the Professional Audio Manufacturers Association (PAMA).

Both he and Sennheiser’s Ciaudelli acknowledge broadcaster concerns that the power and bandwidth issues could cause problems. “There were broadcasters who feared that a WMAS system could show up at a breaking-news site and just wipe out half a dozen ENG crews,” Ciaudelli explains.

On the other hand, Moorut opines that too many restrictions would limit the new technology’s usefulness to all users. “What we saw was that, if you restrict the bandwidth to just 2 MHz, for example, you cannot really leverage the benefits you get from a wideband, 6-MHz system, like the diversity[-signal] benefit you can get when you’re using a full wideband system.”

“This is why Shure advocated for higher power of 100 mW for unlicensed WMAS,” he continues, “which is twice the power allowed for legacy narrowband systems. Since, the FCC did allow 100 mW in their rules.”

After more than two years of agency, manufacturer, and broadcaster back-and-forth over specifications, the format not only seems to allay most apprehensions but also, Moorut stresses, helps defend against potential future reductions in spectrum availability.

“This solves a problem that started with the spectrum auctions decades ago,” says Ciaudelli. “It has been met with wild enthusiasm because it solves so many problems. It became harder to find multiple vacant channels, so a production that used to require four to six vacant channels can now often be done with a single vacant channel.”

Delivery timetables will vary, but products are expected to hit the market by Q1 or Q2 2025.

Although the technical and bureaucratic gestation was typically lengthy, WMAS arrived almost fully formed as a result of that process, suggesting that competition will be immediate and vigorous. As FCC Chairwoman Jessica Rosenworcel pointed out in a statement during the Open Commission Meeting in February 2024, “When a new technology comes along with the potential to improve the efficiency of wireless-microphone operations, we’re going to take a second look. That’s why, a few years ago, we issued a rulemaking to explore this new type of technology known as WMAS, [which] can significantly improve the efficiency of wireless-microphone operations. … That’s a spectrum win-win.”

EDITOR’S NOTE 11/11/24: A quote in this article from Moorut was revised for clarification.