Monday, September 22, 2008

Digital Microphones

Disclaimer: At present I don't own a digital microphone and have not used one either. I have worked with the Nexus installation at the Konzerthaus in Berlin in 2004, and it was a very interesting experience.

How does a "digital microphone" work?

You take the output of the capsule and feed it directly to a high-resolution ADC [Analog Digital Converter] that is designed to optimally complement the capsule. Optional DSP processing allows for transient suppression, limiting etc, and since the standard also calls for information flow to the microphone, various parameters are remote-controllable, including the ability to change the characteristic of dual capsule systems.

Some history...

In 1996 Beyerdynamic premiered the MCD 100 based on an 24 bit Stage Tec TrueMatch ADC - with a true dynamic range of 22 bit. The Berliner Reichstag was equipped with 200 copies of a simpler version, the MCD 803, after which Beyerdynamic retired from that stage. The first microphone to implement the AES 42 standard was the Neumann D-01 in 2001.

An important concept in this regard is gain ranging: Every ADC has an optimal range for incoming signal-levels. In the case of Stage Tec's TrueMatch technology the signal is amplified by +-00, +20, +40 and +60 dB and fed each to it's own 28 bit ADC. A subsequent DSP-unit then picks the optimal representation and digitally scales it to match the continuous output.

Here is a list of companies currently manufacturing digital microphones (in alphabetical order):

Microtech Gefell MV 230 digital
- Measurement microphone

Neumann Solution-D
- Uses a two-tiered approach to optimizing the ADC-input
- Connected though the DMI-2 digital microphone interface

Oktava MK-012 USB preamp
- USP output only, no support for AES 42

Schoeps CMD 2U
- Puristic (non-DSP) approach
- No adaptive gain ranging
- No Mode 2 support for reasons of simplicity

Sennheiser MZD 8000
- Designed from the go to support 2 channels, according to AES 42

The DMC-842 by RME is an 8-channel interface and controller designed to work with all AES 42 compatible digital microphones.

Any concerns anyone?

I wonder if the capsules themselves are linear with regards to their frequency response. When you have a look at the companies manufacturing modular systems this should not be much of a problem as their preamp is designed to work with their selection of interchangeable capsules. With other manufacturers it could be an issue though.

I personally am very happy with my interfaces by Metric Halo.
  • They feature very well designed microphone preamps that I don't have any issue with sonically or handling-wise.
  • The adjacent ADC's are very transparent.
  • Metric Halo's 2d has had a great impact on my workflow, optimizing it in many respects.
I can not image myself lugging around a dedicated controller for digital microphones, but having a few that I can run into my interfaces' digital inputs is conceivable.

OTOH, have a look at Zaxcom's wireless digital systems...


Blogger matt said...

Hello Andrew. You can find a list of additional digital (USB) microphones here: USB microphones

22 September, 2008 18:38  

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