Monday, February 11, 2019

Desk mics go beyond the operational ceiling - AV Magazine

It may well be that signal-to-noise ratio (STN) is the single most important issue in live audio, and nowhere does it topple your ‘audio Jenga’ more than in conferencing.

Forgotten what it is for the moment? Simply the blend of good signal (in this case, voices) with background noise down a mic channel: 80 per cent voice to 20 per cent hiss, hum and general acoustic flatulence is obviously much better than 50 per cent of each, especially as both will get louder if you turn it up.

In performance and presentation, the traditional microphones used are handheld, lapel or headset. They single out the user in a way incompatible with democratic intercourse, and in non-professional hands can create a lot of unwanted noise. You might think a lot of unwanted noise is going to happen anyway, but for a long time everyone was very happy with two other main types of microphone each designed to be mounted on the desk or desks around which the scheduled noise is generated.

The first is the boundary mic which squats flat on the tabletop like a mouse. Examples include the Audio-Technica PRO 44, the MXL AC404 USB and the circular Philips 9172. The second is the gooseneck mic, dotted about the table and protruding towards the seated delegates – such as the Weymic G109, the Shure CVG18 and the MXL AC-400. A third option and a slightly different concept: speakerphones work like boundary mics and are by definition integrated with communications networks, usually exploiting VoIP.

They all have the advantages of no physical contact; cost-effective distribution between several people; and of being fixed in place after installation. However, they do exhibit a wide variation in gain according to the random postures and gestures of the delegates – and this will affect STN, which depends on a short distance from voice to transducer.

Boundaries especially are also subject to interference from actions and objects on the desk: they can be smothered by stationery; knocked into creating nasty peaks by careless elbows; shielded by open laptops; and polluted by machine noise. This is avoided by goosenecks, which also produce better STN provided they are properly addressed, but they too are affected by proximity and one unique drawback: some people find them intimidating and intrusive, and user frustration can even lead to rejection and damage. In the heat of the moment, it has been known.

Theoretically solving most of these problems, along came the ceiling microphone and also the ceiling array microphone. The former might be individual models such as the 360° Polycom HDX, the ClearOne Ceiling or the simple Beyerdynamic Classic BM – is it a microphone or a sprinkler? – but the arrays now include a generation of mic-plus-DSP that raises the bar in terms of accuracy and, therefore, STN.

The plus points are many: complete freedom of movement for the delegates; no intrusion into personal space or social configuration; they cover the whole group using multiple ‘lobes’ to pick up various sections of the room; they are permanently installed; and they are beyond the reach of dropped portfolios, flailing hands and everyday tantrums.

They are some distance from the mouth, though – so how about that STN? This is where the DSP comes in: because the latest models have some kind of on-board noise reduction processing, complemented by beamforming technology that can be programmed to target specific sources or set to track a source automatically.

For example, Audio-Technica’s ES954 Hanging Microphone Array can be focused in 30° increments, while Shure’s MXA910 Ceiling Array Microphone, which actually looks like a ceiling tile, boasts ‘steerable coverage’ that provides eight discrete lobes to cover the room.

But there’s more. This year’s InfoComm saw the launch of Sennheiser’s TeamConnect Ceiling 2. It combines ‘automatic adaptive beamforming technology’ with Dante networking and Power-over-Ethernet, and supports Sennheiser’s Control Cockpit software for remote management, configuration and monitoring – the ‘adaptive’ bit meaning auto-adjustment in order to maximise gain before feedback.

Adam Brown, business development manager at specialist AV distributor POLAR, has something similar up his sleeve. “Beamforming focuses on one position,” he says, “but many rooms today have demountable or divisible furniture and formats and, in any case, people move about a lot more informally. So the Biamp TCM-1 Beamtracking Microphone has eight capsules in array that search and correct gain structures dynamically, using the DSP. You don’t need a transmitter – it’s scanning 360° of the room and making comparisons.”

This is clever, but it’s not perfect. The only foolproof way of ensuring optimum STN is to place a microphone transducer right in front of the lips of every participant in a meeting, so unless you’re willing to pay for and fit theatre-style headset mics to every talking head it ain’t gonna happen. Does the Board of Directors at Barclays want to look like the cast of Les Mis on a Monday morning? Maybe, but don’t expect the gap between the rich and the poor to lessen as a result.



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