Historically, manufacturers worked around this limitation through companding: compressing the bandwidth prior to transmission, then expanding the signal back to full range after reception. Over the years, companding technology has advanced to the point where the top wireless systems are difficult to tell from a wired microphone except in critical, high-definition applications. Companding systems were refined to minimize audio artifacts. Notably, Shure developed a variable ratio companding system. Lectrosonics developed a digital hybrid wireless system that eliminates companding entirely, manipulating the signal in the digital domain while transmitting in the analog.
But, while virtually every aspect of production and consumer electronics — including broadcasting itself — has gone digital, wireless microphones (like their wired counterparts) have remained, in the main, stubbornly analog. And with good reason.
The technical challenges required of a professional digital wireless system are considerable. The number of simultaneous channels required for most productions has exploded, with literally hundreds required for a major event. The latency inherent in process of converting analog audio to digital (and back), if excessive, creates monitoring issues for the performer, and synch issues downstream. And, in the meantime, there has been great uncertainty in the fate of available spectrum.
Digital audio didn’t really come of age in terms of fidelity until the early 2000s. Faster, more powerful chips enabled higher sampling rates and great bit depth, and A/D/A conversion got a lot faster. Soon, digital signal processing became the norm, moving from special-purpose devices, like reverb simulation, into the full range of professional audio equipment, including mixing consoles.
Digital wireless, however, was slow to develop. Zaxcom came out with its digital wireless system in 2001, followed by the Lectrosonics digital hybrid system in 2002. While successful, these products did not really hit the mainstream, and the major wireless manufacturers (AKG, Audio-Technica, Sennheiser, Shure, Sony) were conspicuous by their absence.
But there is no stopping progress. High-end digital wireless offers features that analog can’t, such as encryption and on-board DSP, and the promise of compander-free operation holds out hope of “like a wire” audio performance. So, while analog wireless remains the industry standard, digital system are now being introduced regularly, ranging from low-priced systems aimed at Johnny Rock Star to full-featured professional systems boasting digital outputs and costing thousands of dollars per channel.
At the high end of the market, we see Sony Digital Wireless and the AKG DMS 700. Both offer full encryption and a choice of analog or AES digital outputs. Audio-Technica’s SpectraPulse system, with a unique transmission system intended for fixed installations, has been well received in boardroom and government circles. Lectrosonics came out with its four-channel, point-to-point digital wireless system a couple years back, and Zaxcom continues to expand its vision with such advances as multi-channel transmitters and on-board recording.
The live sound market has seen low-price models introduced, most notably the Line 6 XD-V Series and the PGX Digital from Shure, both at less than $500 per channel. These offerings do not offer encryption or digital outputs. However, the Line 6 offering is interesting for its ability to “model” the qualities of many popular microphones.
Additional offerings abound. Shure just-introduced ULX-D system, said to exceed the performance of high-end digital systems for a fraction of the price. AKG has the DMS70, with all of the audio performance of the DMS 700. And, it’s clear there are more to come, with Sabine SACOM and MiPro ACT having been announced additional new entries to the market.
This indicates that the considerable technical barriers to digital wireless have, largely, been overcome. Latency has been minimized, even while running a 24-bit, 48kHz resolution. The ability to run dozens of systems simultaneously has been realized. And advanced features like 256-bit and 512-bit AES encryption bring a level of security that analog systems lack. While this brief overview can’t fully survey the range of available products and their features, it’s clear that digital wireless is a rapidly expanding product category that bears watching over the next few years.