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of the filters in the receiver. The more the system costs, the better the performance in most cases. And, lastly, good RF coordination will ensure the successful deployment of a large wireless system. BUT WHY DO YOU NEED DIGITAL WIRELESS, IF YOUR ANALOGUE KIT WORKS FINE RIGHT NOW? Two words: spectral efficiency. Demand for wireless microphones increases year-on- year – while the amount of clear spectrum available is shrinking. More mics in less space means it’s going to get crowded quickly, and the amount of radio ‘space’ each channel takes up must reduce to keep up with demand. Wireless spectrum, after all, is a finite resource. If the demand for wireless products increases at the current pace, all users will need to be more spectrally efficient (including consumer goods). It’s a bit like lanes on a motorway: previously we had, say, eight lanes, and only three large trucks needed to run simultaneously – not much traffic and plenty of space. Now, we have four lanes, trying to run 20 trucks side-by-side. Using efficient digital systems, it’d be like running 20 very narrow trucks in the same four lanes; a solution that will actually work.
BEHIND THE SCENES A sound engineer mixes audio from Shure’s TwinPlex subminiature omnidirectional lavaliers
BUT HOW DOES THE AUDIO COMPARE?
use what is typically a proprietary form of digital modulation to send this data. As the transmitted data is digital, the receiver can perfectly recover the digital ones and zeros, resulting in a perfect reconstruction of the original analogue sound – and avoid picking up noise. This also allows the frequency response to be much wider than analogue, as we are no longer bound by the limitations of FM modulation. DOES DIGITAL MEAN NO INTERFERENCE? For UHF-based digital wireless, coordinate your system to avoid external sources or interference in the same way as an analogue system. The advantage is the spectral efficiency; if there is interference, you are more likely to avoid it, because the ‘footprint’ of digital wireless is far smaller than analogue. Therefore, there’s more space to operate. More advanced digital systems like Axient Digital have frequency diversity built- in. This permits two bodypacks to be used on two channels as a pair – to mic up one presenter, for example. The audio from both packs is assessed by the receiver, and at any one moment, the best quality audio is routed to the receiver’s outputs. If pack one goes bad, the good pack’s audio remains on.
The age-old analogue vs digital question is always laced with subjectivity. For wireless mics, though, it’s more objective. On the whole, digital radio microphones will have more low-end and top-end than analogue – and arguably sound more transparent. This is for a couple of reasons. Analogue systems are bound by the limitations of FM modulation, such as limited frequency response. The lack of top-end is particularly noticeable on bodypacks used for instruments with lots of high-frequency content. The frequency response of our digital systems is 20Hz-20KHz, which results in a very full sound. Also, digital systems aren’t subject to noise picked up while being transmitted. In a digital transmitter, the first process applied to the incoming audio is the analogue-to-digital conversion. Now, the audio is represented in ones and zeros, the transmitter will
SUPPLY AND DEMAND The ADX5D is Shure’s response to the industry’s need for digital portable wireless
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39. SEPTEMBER 2021
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