24 September 2009
At the end of 2006 I went over to Neumann, Berlin to be shown the new range of digital microphones and initially was thinking – digital microphones, great, but…
However, I was forgetting about all the headroom that you have to allow for with analogue microphones. Headroom in the microphone pre-amplifier (and the additional noise in the analogue circuit) and the headroom you have to allow in the D/A converter. These two added together mean there is about a 25dB reduction in the s/n ratio – so, a 130dB dynamic range gets reduced, in effect, to only 105dB. That was point #1 that started me sitting up and listening.
The A/D in the Solution-D series (including the KM-D) is a patented Neumann true 28-bit conversion that gets the full dynamic range of the microphone – this is outputted as a 24-bit signal in the AES42 format. The interface controls the microphones and outputs the signal as standard AES3. Details of all this – AES42, Stephan Peus’s paper on digital microphones and product brochures can all be downloaded in pdf format from the Neumann website here.
Once the signal is in the digital domain in the microphone you can adjust the level, add compression, pre-
attenuation, etc., even switch the microphone’s power light on and off or change the brightness. This is all controlled by the Neumann RCS software included with the DMI-2 (see channel strip below).
And there is a lot more you can do in the digital domain in the microphone. Most important (and convincing point #2 for me) is the inclusion of an integral digital limiter that prevents overload. On a test with a microphone with this disabled, is was very clear how effective this limiter is. No distortion at all, it just does not get any louder. Great for transients that would normally distort the recording and require a re-take – now it’s just perfect.
Those are the main reasons why I immediately put my own money on the table and bought my own pair of the KM 183-D diffuse-field omni microphones and I have also now purchased the KK 131-D flat-omni (nearfield) capsules as well.
The Project
I had been asked to record a series of CDs for the pianist, Richard Meyrick. I have recorded Richard many times over the years, normally with Sennheiser MKH 20 omnis – but this time I also used the new Neumann KM 183-D digital microphones.
The project was sponsored by The Man Group and Blüther pianos, so our hands were not tied to get a good sound.
The recording venue was The Menuhin Hall in the Yehudi Menuhin School in Stoke d’Abernon. This is a superb building with a great sound. It is totally isolated from outside noise with a perfect cable route to the Green Room where we set up the recording equipment.
AES42 signals can travel good distances along normal microphone cable, but twice as far over AES cables; so I went along to Canford Audio and got them to make me some custom cables (yes, I know - I’m lazy and I am not proficient with lead-free solder yet) made with proper balanced AES digital audio cable, terminated with the new Neutrik EMC XLR connectors. AES42 at 24/96 can travel about 200-metres along these cables, so distance was not a problem.
As this was my first outing with the KM-D series, I did a parallel recording with a pair of MKH 20s (as you can see in the picture).
The microphones were set up as shown in the photo. As the KM 183-D is a diffuse-field omni, it has a lift in the upper frequency range. But I had the microphones only about a couple of metres from the piano. Anyone who has seen a polar-pattern of an omni microphone knows how the high frequencies are attenuated off-axis due to the physical size of the microphone. We started with having the 183-Ds at about 45°, but found this was still a bit too bright; so we turned them through 90° and had them vertical. At this position the frequency response was ruler flat and the piano sounded great (the MKH 20s didn’t need turning as they have a flat response head on).
The KM 183-Ds were connected to the Neumann DMI-2 interface which locked them to the same clock time. They were set to a 96kHz sample rate and a digital gain of 25dB was applied (in practice this was fine as the absolute maximum peak ended up being about -1.6dBFS – I ended up not needing the limiter at all). I did not apply any compression at all.
The output of the DMI-2 was fed to an AES splitter which outputted to a Fostex FR-2 recorder for the main recording at 24/96. The second output went to an Audio Design ProBox 10 sample rate converter which down-converted to 16/44.1 to record a DAT safety copy on my old Fostex D-10. The MKH 20s went to an Audio Design DMA2 24/96 mic. pre. and into a second FR-2 (kindly loaned by SCV London for the event).
Monitoring was via a Grace m902, Sennheiser HD 650 headphones and Klein + Hummel O110 active monitors (as shown in the picture). Talkback was via my custom unit (made by myself many years ago) which also controlled the red lights. I also used “The Box” for stereo soundstage imaging.
The first recording session was five consecutive days just before Christmas ’06. The sessions went extremely well and the microphones behaved flawlessly. We were delighted with the results.
The KM-D microphones are so quiet that we had no background noise “clue” when we were playing back. We kept thinking something was wrong, as every time we started to play back a take we couldn’t hear anything – until the music started. They are quiet!
The sound of the microphones is the sound of the capsules with nothing added and nothing taken away. Once we had tamed the top end by angling the microphones correctly, everything was wonderful.
After the session, we spent a weekend with Sequoia on the PC, editing most of the sessions and the pianist and sponsors are absolutely delighted with the results.
In total we had four recording sessions and the final result was for CDs with an initial run of 3,000 of each.
Yes – we chose the KM 183-D microphones for the release (not that the MKH 20s weren’t good – but this combination was the best one in this situation).
I don’t spend my own money lightly - probably something to do with my Scottish great-grandmother - and I certainly have no regrets in doing it this time.
In fact the KM 183-Ds work out quite cheap – including the interface, a pair works out at about the same price as any top class omni (slightly cheaper than a pair of MKH 20s) – but when you factor in that you don’t need a mic. pre. or A/D, or even a limiter / compressor…
And - when the mixer and DAW manufacturers come out with AES42 inputs on their equipment, you won’t even need the interface.
The CDs we released can be seen on Richard Meyrick’s website here.
You can read Hugh Robjohn’s review of the KM-D series (published in the March 2007 issue of SOS) here.
Full details on the KM-D series are on the Neumann website here.
I also came across this informative video by Neumann on YouTube:
Many people have questions about digital microphones, so here’s the place to ask them…
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Tags: analogue microphones | D/A converter | digital limiter | digital microphones | dynamic range | Neumann | omni microphones | pre-amplifier | pre-attenuation
The sound of the microphones is the sound of the capsules with nothing added and nothing taken away. Once we had tamed the top end by angling the microphones correctly, everything was wonderful.