Digital, surround microphones at AES 2010

Educational sessions on digital and surround-sound microphones were some of the highlights of last week’s AES convention in San Francisco.
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The 32-element Eigenmike from mh acoustics is shown here in its windscreen version.

The129th AES convention was well attended, at least better than last time when it was held at the beginning of the economic downturn. The exhibit hall contained vendors from around the world demonstrating a wide variety of microphones, processors, vacuum tube equipment and mixing boards. The constantly busy booths suggested that the audio industry was starting to pick up.

The educational sessions covered a range of topics from loudspeaker design and the effects of digital processing to the transport of live music and the problems that it creates, among many others.

Digital microphones

In today’s world all signals are digital, a concept that is being extended even the lowly microphone. In the product design session “AES-42 Digital Microphones,” discussion centered on the standard itself, the difficulties in design and the advantages of a digital microphone.

The real difficulty is in getting the dynamic range of the microphone into digital. This requires a unique sort of digital-to-analog converter. Getting a full 24-bit dynamic range, which equals 144dB, is the real trick. With this kind of range, no gain control is required on the recorder because the input will never be overdriven.

5.1 microphones

One of the first sessions I attended was “Single Unit Surround Sound Microphones,” where six different manufacturers talked about and showed off their own systems. Problems of workflow were discussed, including the fact that many camcorders only have four audio channels with two reserved for talent, making it hard to capture 5.1 surround sound. (AES is working on a standard for multichannel microphone connectors and cable.)

And, there was some disagreement on whether surround sound should be introduced into the center speaker, where the main announcer’s voice is placed. Discussion focused on the concept of B-format encoding/decoding, which would enable a complete surround-sound signal to be transported over a minimum of three channels. The mid/side stereo microphone technique, used in several of the microphones shown that allows the pickup pattern to be manipulated after recording, was also discussed. Using just three microphones to pick up 5.1 surround allows for smaller microphone size, which is good for such work as documentaries. Almost all the microphones allow recorded signals to be manipulated in post so as to direct the sound and widen the stereo effect. The amount of control over the sound was very impressive.

Mh acoustics started with the Eigenmike, a sphere-shaped unit with 32 elements all around. Once recorded, it can direct the sound pickup anywhere in a 360-degree pattern. An offering from DPA Microphones, Model 5100, looks like nothing more than a bicycle seat. Its triangular shape and relative small size allows for it to be mounted on top of a camcorder, and it outputs in discrete 5.1 analog. Sanken was next with a microphone that actually looks like a microphone, containing several elements within its frame allowing it to pickup a full 5.1 surround pattern. Schoeps showed its four-legged microphone meant for surround pickup and requiring a very large windscreen cover. SoundField had its four-element surround-sound microphone and associated processor, and Josephson Engineering showed its three-element microphone using a form of the mid/side pickup technique.