The Future of Wireless Audio

The Future of Wireless Audio posted: 23/02/2023

Wedemark, February 2023 - Alignment meetings with regulatory bodies, demonstrations to high-profile wireless users and decision-makers - is there a new type of wireless audio transmission on the horizon? While the rumour mill is leaking some details here and there, four Sennheiser experts reveal what this new technology is about. Dr Andreas Wilzeck (Head of Spectrum Policy and Standards), Martin Brandenburg (Project Manager), as well as Dr Sebastian Georgi and Jan Watermann - the two research and development engineers who are the inventors of what is called Wireless Multi-Channel Audio Systems (WMAS) - dive into the benefits of the technology and explain how it will change the wireless landscape.

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Gentlemen, you are working on a new technology called WMAS, wireless multi-channel audio systems. What is this technology about? Who is it for?

Sebastian: With this technology, we are re-thinking wireless transmission in multi-channel applications such as big live events, theatres, and broadcast studios - wherever many audio channels are up in the air. Sennheiser's implementation of WMAS is essentially a bi-directional wireless broadband technology, which combines microphones, in-ears, and remote control in just one broadband RF channel.

When we started out with this development project, our original intention was to combat RF fading, the natural signal loss on stages. RF fading can cause signal dropouts, which is what makes every sound engineer's job so difficult. By finding ways to better exploit the diversity offered by the broadband RF channel, we wanted to eliminate the risk of signal dropouts.

In addition, we aimed to simplify set-up for the user, acknowledging the fact that narrowband wireless systems require quite complex stage set-ups, especially in multi-channel applications.

Another goal was to make better use of the scarce frequency resources, an ever-increasing challenge that audio engineers are faced with.

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TV channel usage (6 MHz) of several narrow-band systems (left) and a WMAS (right), which assigns time slots instead of fixed frequencies. The blue and grey lines are the attenuation (in dB) of the measured receive signal of the exemplary antennas 1 and 2

What is the difference of this broadband approach compared to today's wireless microphone systems?

Jan: Today's wireless audio technology relies on narrowband RF solutions, with one transmitter sending signals to one receiver unit. And, unfortunately, the transmitter cannot notice whether its' receiver has been switched on or not, or whether it is out of range. In a figurative sense, you could say that every microphone, once configured, is fighting on its own.

Broadband wireless technology, on the other hand, is system-based, a cooperative approach, as it were. Many mobile devices are linked over the air with one rack-mount unit. Now, everything happens in a single broadband RF channel with a bandwidth of 6 or 8 MHz, the bandwidth of a TV channel. The audio engineer simply selects a carrier frequency for the broadband RF channel to be configured, and the system will coordinate itself, with the quality and range that the engineer chooses for the individual audio devices.

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That sounds amazing, but does a solution that occupies a full TV channel - so 6 or 8 MHz of RF spectrum depending on where you are in the world - really save frequency resources?

Martin: It does indeed. Just bear in mind that WMAS is designed for multi-channel audio applications that integrate wireless microphones, in-ear monitors, remote control, and other audio applications into one radio interface. This brings significant efficiencies in spectrum use - not just by technology, but also by enabling workflow improvements. These wins can be invested in flexibility and audio quality. For example, IEMs and microphones, which today are split between two RF ranges that are several MHz apart, can now be handled together in a single TV channel, which, in addition, makes frequency planning a breeze. But to be clear, narrowband, 200 kHz digital wireless microphones will continue to be used for applications where this integration is not required, or where only a few mics are used.

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Secondly, our system will operate with a total of 50 mW of transmit power per RF broadband channel, which is the transmit power of a single microphone today. Within the capacity limit of the system, there will no longer be any scaling of the total transmit power by the number of devices used. Furthermore, this transmission power will be distributed over the entire RF broadband channel, so the spectral power density is lower by a factor of 30 (6 MHz) or 40 (8 MHz) compared to a single wireless microphone with a bandwidth of 200 kHz. This low spectral power density means that an RF channel can be reused more easily. This would, for example, be an asset in multi-studio broadcast production facilities or on the different stages of a spacious festival site.

Last but not least, our approach allows remote control of all equipment at all times, and also the allocation of resources to equipment as really needed at any given time. This makes it possible to save spectrum by employing a new workflow where the audio engineer can schedule resources on a timeline. Compared to today, where all devices would be actively transmitting at the same high quality all the time, this new workflow would mean a substantial gain in spectral efficiency at large events.

Overall, the Sennheiser solution will enable customers to significantly reduce their spectrum footprint while gaining unmatched integration, audio quality, low-latency transmission, control, and flexibility in their applications.

Andreas: It is worth noting that the number and complexity of large events

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