Notably, Shure recently unveiled our first WMAS enabled product line, Axient Digital PSM, a digital wireless in ear monitoring solution that has been meticulously designed and developed to adapt to a wide variety of environments. The system features a multichannel wideband mode that significantly increases spectral efficiency, freeing up radios for improved radio frequency (RF) performance or channel count scalability (Figure 1).
While approaches to implementing WMAS will differ and evolve, understanding the new regulatory framework and how it coexists with current digital RF systems will allow audio professionals to fully benefit from the advancement’s potential.
Understanding WMAS: Advancements in Wireless Audio for PMSE Applications
WMAS is a technology-neutral approach for wireless audio that supports multichannel audio applications. In the regulatory world, this application space for wireless is often referred to with the term Program Making and Special Events (PMSE), which includes broadcasting, news gathering, and a broad range of cultural and business events from concerts to conventions. Across all these applications, wireless links are critical to deliver the expected production values, audio quality, and visual aesthetic. And since all wireless links need spectrum to operate, any change in the way spectrum can be used is a big deal with implications for wireless microphones and in-ear monitors (IEMs).
In particular, recent WMAS regulations allow for an RF signal to occupy a wider bandwidth than under previous rules. This greater bandwidth allows next-generation technologies to offer advantages such as increased audio channel capacity in a given range of spectrum, a variety of service levels, and easier deployment. At Shure we are always looking for more efficient ways to use spectrum and to develop tools for users to optimize whatever spectrum they have available for the needs of their production. The variety of use cases in professional audio is such that no single transmission scheme will fit every job, but a WMAS approach can offer compelling flexibility, especially when higher channel counts are required. While the regulatory discussions around WMAS are progressing in different states around the world, this is definitely an exciting time for wireless audio, with the potential to open new possibilities and applications.
Figure 2, from the European Telecommunications Standards Institute’s (ETSI) technical report, illustrates typical audio PMSE solutions that can be implemented utilizing WMAS.
One way WMAS can help make better use of available RF spectrum is by reducing the space between the transmitted audio channels and placing any intermodulation products within and underneath the level of the primary signal. This is done by combining multiple audio channels into one wider channel. This can be visualized in Figure 3.
WMAS systems can share the spectrum with narrowband systems, but some planning and coordination will still be required. While current narrowband systems use 200kHz per channel, WMAS opens up a range of potential bandwidths. The total width of the signal could be as much as 20MHz (depending on regional regulations and frequency range), although it doesn’t have to be. There is no prescribed technical approach or specific recipe for transmission scheme if certain basic requirements are met, for example compliance with an emission mask for spurious emissions and capability to support at least three audio channels per 1MHz.
How It Works
WMAS allows for using a wider variety of transmission methods than have previously been available for operation in the UHF TV bands. The physics of the UHF range are particularly well suited for wireless audio, but to access it, PMSE devices have worked within bandwidth constraints that preclude technical approaches used in other frequency bands. One example of such an approach is Orthogonal Frequency Division Multiplexing (OFDM). OFDM is a technique used in many communication systems like Wi-Fi, 4G, and 5G that splits data into smaller “parts” before sending them over frequencies at the same time. This helps the data travel more efficiently and reduces interference.
With OFDM, various channel access methods can be combined to accommodate different users or, in the case of WMAS, individual audio channels (refer to Figure 4). These include:
- Time-based separation (OFDM/TDMA), where each audio channel gets a specific time slot.
- Frequency-based separation (OFDM/FDMA), where each audio channel gets a fixed frequency.
- A combination of both time and frequency separation (OFDM/OFDMA).
- By leveraging the capabilities of OFDM, a WMAS system can effectively serve multiple users (including audio sources and destinations) with the wideband signal and enhance the efficiency and flexibility of audio channel management.
Bandwidth Scalability
Building on the idea that WMAS opens up a range of possible bandwidths, it’s worth noting that the spectrum usage can scale to fit the number of audio channels needed. Depending on the implementation, hardware can be designed to support both narrowband and wideband modes, which can strike a balance between realizing the advantages of wideband and the granularity that narrowband offers when coordinating in a complex or congested RF environment. This means a WMAS system can work alongside traditional narrowband systems or use a bandwidth appropriate for the available free spectrum. Figure 5 shows three examples of how this flexibility can be applied.
Coexistence: WMAS and Narrowband, the Best of Both Worlds
When using WMAS, it’s important to consider the number of audio channels needed and the available free spectrum. If only small gaps in the spectrum are available, narrowband systems might be better, especially if you only need a few audio channels. WMAS works best in setups that require many wireless microphones or IEMs.
Like narrowband systems, WMAS needs careful frequency planning:
- Find large enough gaps in the frequency spectrum.
- Consider the WMAS RF bandwidth.
- Ensure it works well with narrowband systems.
It’s important to note that you cannot use narrowband and WMAS systems on the same channel. To maintain reliable operation, a minimum spacing between narrowband and wideband systems is necessary.
Shure’s Approach to Next-Gen Wireless Audio Technology
It is Shure’s philosophy that WMAS is an additional option, not a replacement for traditional narrowband systems, and is useful for professional setups needing multiple audio channels.
Bandwidth scalability is key to achieving this coexistence, it means a WMAS signal can occupy less than a full TV channel, be a good neighbor to incumbent narrowband systems, and allow users to be more granular as they make optimal use of the spectrum available to them. Shure fought for higher maximum output power limits to support reliable operation per user in a multi-user signal without excessive occupied bandwidth. Scalability can refer to both number of users and use of spectrum.
This approach is reflected in Axient Digital PSM, Shure’s WMAS-powered digital wireless in-ear monitoring system that was referenced at the beginning of this article. Axient Digital PSM can scale up to 28 independent stereo channels per 6MHz and 40 independent stereo channels per 8MHz in Europe. That is industry leading spectral efficiency! Axient Digital PSM also offers a narrowband mode to access more radio frequency output power for greater range. This scalability and flexibility allow engineers, and production and equipment providers to address their needs today while being prepared for the future.
Looking Ahead
Axient Digital PSM is poised to make the most of recent regulatory changes. Users can look forward to a range of benefits as wireless systems evolve, including easier setup and enhanced overall performance.
These innovations will give audio professionals more ways to make optimal use of the available spectrum, make it possible for the additional wireless monitor mix or microphone to go on air when the production needs it and unlock creative possibilities. Shure remains dedicated to leading the charge in this technological revolution, ensuring our products remain at the cutting edge of innovation and reliability. aX
This article was originally published in audioXpress, February 2025
