Anyone who knows me will tell you that I am a microphone freak, so any activity involving microphones is at the top of the gear lust chart for me. There are three thing you cannot have enough of: money, microphones and well, you can guess what else.
I recently had the opportunity to check out Neumann’s TLM 103 D digital microphone system. This is the first time I have worked with a digital microphone, and it is quite a different experience from using an “old school” microphone. At this point in time, the audio industry has analog microphone technology down to an elegant and exact science. We rarely run into problems with phantom power (1) and you can be almost 100 percent confident that plugging a mic into a console’s microphone input will result in sound. In fact I’d dare say that analog microphone technology pretty much matured 50 years ago when Mylar was substituted for PVC as a diaphragm material.
Test 10100110
The digital microphone experience is very different. Neumann digital mics mate with the DMI-2, a small power supply/interface box providing solely an AES output (this is typical of digital microphones). Initially this rocked my world. You mean I don’t get to choose the mic preamp? Nope, it’s built into the mic. Analog-to-digital converter? Built into the mic. What about that $2,000 analog compressor in my rack? Sorry, can’t use it. Ouch. The microphone connects to the PS with an AES/EBU cable — yeah, the ones that look like standard microphone cables, but don’t use an analog cable because, while the XLR3 connectors are the same, the impedance of the cable is not.
Shockingly, the DMI-2 has no external controls. Nothing. Not even a power switch (very unnerving). So I’m looking at this thing thinking, “how the heck do I set the gain?” Ah, there is a software CD in the box. If these guys did not make this thing Mac-compatible, someone is going to get a box filled with stinky socks on their desk. It is Mac-compatible, thank you very much. A small adapter is included with the system which mates a USB cable from my Mac Pro to something that looks like an Ethernet connector on the DMI-2.
Neumann’s software for their digital microphones is called RCS (Remote Control Software), which does exactly that. Here is where we find controls for microphone gain, low-cut, compression and “digital phantom power” on/off. As you’d expect of a condenser microphone, power is required to bias the capsule and run the internal electronics that include the DSP and A/D conversion.
All of this data is exchanged (both directions) via the “mic” cable. Lucky for us, Neumann knows a thing or two about microphones as well as electronic standards. They helped develop the AES42 specification which defines parameters for the transmission of digital phantom power to the microphone (+10V for the curious) as well as for implementation of gain adjust, low cut filter, compressor, limiter, phase reverse and pattern control for mics that offer that ability. In fact, Neumann RCS and the DMI-2 can be used with any digital microphone that conforms to the AES42 standard.
But Why?
What’s the advantage? Converting the audio signal from analog to digital information at the source negates the effects of frequency response degradation due to cable capacitance, and greatly reduces the chances of interference from RF. Conversion to digital directly from the capsule also eliminates several analog gain stages, and where there is gain, there is potential for noise. Analog devices in the chain such as mic preamps, EQ and A/D converters are (for better or worse) eliminated from the signal path so the requisite impedance and level matching between these devices is no longer an issue.
And who, you might ask, actually makes digital microphones that conform to the AES42 standard? Sennheiser and Schoeps, for starters (we were unable to confirm whether or not the MCD100 from beyerdynamic supported AES42). Earlier this year Sennheiser announced the MZD 8000, an accessory for their MKH 8000 series of modular condenser microphones. This device replaces the analog preamp/body of the MKH 8000 mics. You simply screw the capsule onto the MZD 8000 and you now have an AES42 output. This is a fantastic idea — you can have mic capsules for use with either traditional analog circuitry, or with the AES42 digital standard.
Schoeps is also in the race for AES42 with the introduction of their CMD 2U digital microphone preamplifier. This preamp conforms to AES42 and is compatible with the entire Schoeps line of Colette Series capsules, which currently number around 20. You could conceivably have a CMD 2U preamp for digital recording and a “standard” analog preamp for when you need to use that vintage Neve 1073 preamp/EQ you covet.
Where does this lead us? To a digital console, naturally. It only makes sense that we have started to see and will continue to see an increase in the number of digital consoles that can accept AES42 input. As of now, Innovason supports AES42 via their DioCore and Stage Box, which interface with their Sy48 and Sy80 digital consoles. At the NAB show in Las Vegas, it was announced that DiGiCo digital desks now have the ability to directly interface with Neumann digital microphones. I expect that it won’t be long before we see more manufacturers offering digital microphones and digital consoles with AES42 compatibility. Keep a close eye on that XLR mic input: it might not be exactly what you expect.
[Garret, put the text below in smaller footnote font, with a superscript “1” instead of the (1); it refers to a footnote in the second paragraph]
(1) I have found one issue with phantom power: certain manufacturers do not adhere tightly enough to the 48 V DC phantom standard. There are certain microphones that will operate over a range of phantom power voltages (the Shure SM81 for example) and as a result, certain console manufacturers have made the decision to designed their mixers to deliver phantom voltage lower than 48 V. However, just because a microphone can be run on say, 18 V DC does not mean that it should be run on 18 V DC. The reduced voltage yields less headroom and an increase in distortion. Further complicating the matter is the fact that phantom voltage lower than 48 V DC is insufficient to power certain microphones, period. The Neumann U87i, Audix SCX25A, Earthworks TC25, and Audio-Technica AT4050 come to mind.
Steve “Woody” La Cerra is the tour manager and Front of House engineer for Blue Öyster Cult.
