Sunday, February 3, 2013

Schoeps SuperCMIT DSP-steered Digital Shotgun Mic


Schoeps Super CMIT
I just started seeing the unmistakable Schoeps blue shotgun recently on TV during some media circus press event. It was probably the earlier analog version, but the point is, since no other mic has this blue metallic finish, Schoeps gets “recognition points” for daring go other than grey or black. Actually, putting out a shotgun mic, regardless of color, was some thing that Schoeps had not considered until they received solid input from the US market that one would be well received. That’s how the first CMIT came to be.
In another daring move, Schoeps released the SuperCMIT digital shotgun with a two-position, DSP circuit to tighten the pattern and lower ambient noise.

Schoeps isn’t the first with a digital mic. That honor goes to beyerdynamic and their MCD100 that was presented to AES in 1996 and hit the market in 1999. I reviewed, in January of 2000. Beyer followed that with two digital shotguns; the MCD 836 and MCD 837. I’m guessing they are either in a collector’s mic locker or they were trashed because they didn’t work when someone unknowingly plugged them into an analog mic preamp at a hamfest. Shortly thereafter, Audio-Technica showed their AT 895 DSP-steered analog mic to market. *Since then no one has bothered to take a serious crack at DSP-powered mics or digital mics. 

*2/4/13: John Willet reminds me that I need to re-read my reviews that were published some time ago for timeliness. Of course Neumann has followed up with digital mics and I have reviewed two of them. He also reminds me that Gefell released a digital mic. That one got past me. I don't think the Sennheisers were out at the time I wrote this. Here's my review of the TLM 103D.

EQ and Preset Buttons
The Schoeps SuperCMIT has both AES42 digital output and DSP steering. The mic has two outputs. One is the unaltered output of the main capsule. The other is the audio  after DSP processing. In addition to the high boost and low cut filters, the SuperCMIT as a two-position switch that engages Preset 1 or Preset 2. Preset 1 provides a more narrow pattern than the unprocessed pattern. Preset 2 is much more aggressive but useful in situations where the ambient noise is so loud that, regardless of fidelity,  digging any audio out is a challenge. 

There are, however, some caveats as you step through the digital mic doorway. In a digital word, you need a source with an internal clock. The SuperCMIT has that. If you use more than one super CMIT or want to use another clock source, sample rate converters must be used. You may need to convert from its 3-pin XLR AES42 output to an AES3 input with sample rate conversion. In addition, the SuperCMIT requires 10 Volt Digital Phantom Power (DPP). The Sound Devices 788T has both powering and AES42 inputs, no problem. Schoeps has the PSD 2U for powering the mic if your kit doesn’t have this ability. The Zaxcom Deva and Aaton Cantar currently require the DPP but have sample rate conversion. 

Schoeps Mini-DA42
If you have no digital inputs, the Schoeps Mini-DA42 module supplies power and converts the AES42 output of the mic to AES3 and to two XLR balanced analog outputs.  An AC adaptor with Hirose plug is included but you can power the unit by battery in the field. You may consider digital mics and AES42 fringy, leading edge technology, The field is quickly growing. Other gear supporting the AES42 input include the AETA 4MinX, TASCAM HS-P82 (no DPP), RME DMC-842, Lake People DAC C462, Neumann DMI-2 and Zaxcom TRX942.

So, how does this DSP work? Pretty well, actually. There’s a second diaphragm behind the primary diaphragm that faces to the rear. This rear-facing diaphragm senses the off-axis sounds. The two signals are combined in a time and frequency-dependent way to cancel sounds mostly below 5-6 kHz in the diffuse field. If you saw any of the World Cup Soccer broadcasts in 2010, a lot of the sidelines mics were SuperCMIT. It may be time to think about retiring your parabolic mics.

To replicate a video shoot in a normal interior, I first tried the SuperCMIT in my living room at typical dialog boom distances; eight inches to a foot above my head. Listening to both the straight and DSP-filtered versions is somewhat problematic if your listening to your own voice because of the latency created by AD conversion and processing. I routed the mic to the to a Schoeps PSD 2U for DPP and took the AES3 output straight into my Sound Devices 744T. One track recorded the “straight” signal from the SuperCMIT, the other track recorded the DSP-processed output. On a third track I recorded a Sennheiser MHK416.

After transferring the tracks to Pro Tools, I noticed the was a slight timing difference between the two tracks. The Schoeps tracks were a little late due to analog-to-digital conversion and DSP processing. The unprocessed SuperCMIT track sounded less aggressive and more natural than the MKH416; much like the sound I get from my Schoeps cmc641. 

Rejection of distant sound was noticeably different between the SuperCMIT and the MKH416, and not exactly as I suspected. I had both mics on boom stands in my cathedral ceilinged living room. The windows were open. Birds and the relative quiet of a suburban neighborhood were audible. A distant Light Rail train passed and switching back and forth among the three tracks, I found both the Schoeps regular track and DSP Preset One rejected the birds and train better than the 416. At this particular moment, there wasn’t a noticeable difference between the two Schoeps tracks. I had matched the levels, but the MKH 416 is brighter than the Schoeps, as was apparent by simply listening. That elevated HF EQ may explain some of the difference, but not all of it. 

While setup in the living room, I opened the doors of the refrigerator/freezer in the next room, the kitchen. When the compressor kicked in the fan noise was much more audible on the MKH 416 than either track of the SuperCMIT. Both Schoeps capsules generated a slight amount of HF hiss relative to the MKH 416, but you had to be listening in very quiet ambience to hear it.

I left the 416 inside and headed out as I heard the mowing service enter the neighborhood. Three or four gas-powered mowers, trimmers and blowers make a great diffuse noise source. They were thirty to forty feet away. In this assault, the differences of the two Schoeps became more audible. Preset Two did a better job of digging me out of the noise, but there were audible artifacts that sounded like a wide spectrum expander or gate that closed down around the edges of my voice. The artifacts weren’t as audible with Preset One, but my voice was buried deeper in the mower noise. You might not win any audio purity tech awards with Preset Two, but it might be the perfect tool for a media circus. And the nice thing about the SuperCMIT is that you get both straight and your choice of DSP. So if you have time in post, you can apply noise reduction to the straight track. If after using Preset Two in the field, you find it too severe in post, you still have the straight track to work with. That’s a win-win situation. 

Ty Ford may be reached at www.tyford.com

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