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Schoeps CMD 42 - Digital Microphone Preamplifier


VASI

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Hello World,

 

Seems like the beta phase of Schoeps CMD 42 is over and Schoeps gonna release it in April 13th 2024.

 

It is compatibility with all MK capsules and Colette accessories. AES42 Mode 1 & Mode 2.

 

CMD Remote App to handle all the settings.

 

From my limited market research, it has price tag around 1.000 euros. Not sure about dollar price.

 

Wireless Transmitters Compatibility:

 

- Sound Devices A20-TX
- Zaxcom TRX745
- Zaxcom TRX743

 

Screenshot_1.png

 

More information: https://schoeps.de/en/products/colette/microphone-amplifiers/cmd-42-beta.html

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Just what I wanted.  An app for my microphone.  What are the odds we'll be able to resell this PSU in 40 years, given that the full functionality is tied up in an app ecosystem where compatibility is measured in single-digit years?

</sarcasm>

That said ... it does do things that other mics don't normally do, and I can see digital output being occasionally useful.

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43 minutes ago, The Documentary Sound Guy said:

Just what I wanted.  An app for my microphone.  What are the odds we'll be able to resell this PSU in 40 years, given that the full functionality is tied up in an app ecosystem where compatibility is measured in single-digit years?

</sarcasm>

That said ... it does do things that other mics don't normally do, and I can see digital output being occasionally useful.

 

"...alternatively it can be controlled via a AES42 standard interface"

 

😉

 

 

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Is there a more advanced interface for AES42 than what my Nova provides?  How are those advanced features accessed?  My understanding is AES42 is a spec for transferring digital audio (sometimes with self-power), not a control spec.  Schoeps has a list of AES42 interfaces and what features are included, and most of them do not provide more than power and sample rate conversion.

https://schoeps.de/fileadmin/user_upload/user_upload/Downloads/Kataloge_und_Broschueren/Prospektblaetter/AES_42_interfaces_for_Schoeps_CMD_42_and_SuperCMIT_-_Tabellenblatt1.pdf

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1 hour ago, The Documentary Sound Guy said:

Just what I wanted.  An app for my microphone.  What are the odds we'll be able to resell this PSU in 40 years, given that the full functionality is tied up in an app ecosystem where compatibility is measured in single-digit years?

</sarcasm>

That said ... it does do things that other mics don't normally do, and I can see digital output being occasionally useful.

 

Vasi is suggesting that Schoeps will announce this at NAB. Presumably it will address the issue you raise, which is going to be on the minds of a lot of people.

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22 hours ago, The Documentary Sound Guy said:

Is there a more advanced interface for AES42 than what my Nova provides?  How are those advanced features accessed?  My understanding is AES42 is a spec for transferring digital audio (sometimes with self-power), not a control spec.  Schoeps has a list of AES42 interfaces and what features are included, and most of them do not provide more than power and sample rate conversion.

https://schoeps.de/fileadmin/user_upload/user_upload/Downloads/Kataloge_und_Broschueren/Prospektblaetter/AES_42_interfaces_for_Schoeps_CMD_42_and_SuperCMIT_-_Tabellenblatt1.pdf

 

I am afraid that is a question about the end-side (eg. recorder) rather than the AES42.

 

https://sound-link.co.uk/docs/AES - Digital Microphones - AES42 and all that.pdf

 

The only two recorders which support Mode 1 & Mode 2, is Aaton Cantar X3 and Cantar Mini. But it's out of business, oh well. 😅

 

====

 

I would like to see more information about other stuff regarding CMD 42 instead of how to control via end-side (eg. recorder) or to use an app. I hope some stores like Gotham which produce - report videos from NAB to cover some basic questions like:

 

1. Enviroment tempatures and conditions. Currently shooting in a place with -30 Celsious. How it handles such low tempatures or high tempatures like in desert; and if has been tested in such "real life situation". The next question is about humidity and if affect it.

 

2. A20 / 745 / 743 is the only available transmitters for now. Any feedback from beta tester with those transmitters and what the pros or cons.

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Digital Microphones..... a solution looking for a problem.   Neumann dropped their Solution D series and Sennheiser has not made their  digital 8000  series components in a few years.   Mature analog technology is still King. 

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I'm not going to say you're wrong, because you aren't, but Schoeps does say this about why it exists:
 

Quote


The CMD 42 is not intended to replace analog microphones. Rather, it is meant for applications in which its special features offer distinct added value:

  • Immunity to interference: The digital output resists any interference in the cable
  • Dynamic range: No analog level-setting is required; the full dynamic range of the capsule is transferred into the digital realm
  • High resolution: Sampling rates up to 192 kHz and extended frequency range for the microphone capsule beyond 40 kHz ("xt" functionality)
  • DSP: Extensive signal processing is available directly within the microphone, including among other routines:
    • Compressor, limiter
    • "Upmix" to stereo
  • Remote app: Easy control setting via smartphone
  • Two-channel output: can deliver both a processed and an unprocessed signal simultaneously (e.g. as a backup)
  • Flexible function indicator via integrated LED

 

I'd say the latter points are stretching quite a bit, but perhaps the earlier points cover some scenarios where a digital microphone could make sense.  In any case, I'm sure Schoeps is used to making low-volume parts, maybe some people will find it useful.

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There are real-world situations in which a digital microphone can offer an audibly lower noise floor than a comparable analog microphone. For years I used to think that digital microphones were just a rearrangement/refactoring of the same set of components (capsule, preamp, a/d converter) as in a digital recording setup with analog mikes, and yes, that is true for the most part.

 

But the hitch is analog mike preamps (whether outboard or part of a mixer or recorder) and their noise levels and headroom in relation to their gain settings. Mike preamps, contrary to what some people apparently assume, are nearly all at their quietest when set to the upper range of their gain settings. If the sounds that you're recording include very high SPLs (even for brief intervals), you can't leave the gain of the preamp (or analog recorder or mixer input) set very high, or you'll clip the analog electronics. As a result, you have to set the gain for the loudest sound that you expect to pick up, which raises the noise floor for the quieter parts of whatever you're recording, compared to what that noise floor would have been at higher gain settings. Sometimes this raises the preamp's noise floor above that of the microphone or the recording environment. And that's a compromise that you don't have to make with digital microphones.

 

As a result, every now and then people with real, professional experience find to their astonishment that digital microphones are quieter or even (as some have said) much quieter in certain recording scenarios than the comparable analog microphones had been for them before. I used to think those people were tripping--but now I realize that they could very well be describing their experience accurately, though perhaps not understanding that no, the microphones themselves aren't any quieter; it's the benefit of working without the occasional limitations of analog preamps. The effect isn't extremely common, but I think it's 100% real when it occurs.

 

Does that explanation help? There's a video in German that Helmut Wittek from Schoeps posted on YouTube that goes into this; I could provide a breakdown of it in English if anybody wants.

 

--best regards

 

 

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21 minutes ago, DSatz said:

There's a video in German that Helmut Wittek from Schoeps posted on YouTube that goes into this; I could provide a breakdown of it in English if anybody wants.

 

 

Thanks. I’m quite interested. If you could point out which Wittek video, it may be that English translation is available. I just tried “auto translate” on one of his videos, and the translation seems to be pretty good. This would save the trouble of you writing a summary.

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Um, no, I meant https://www.youtube.com/watch?v=2st7KzoEHlo starting at 24:01. This came up last August on an amateur audio forum that I sometimes participate in ("Tapers Section"), where someone had watched this video but perhaps didn't understand the German being spoken, and thought that Wittek was recommending to set analog preamps to low gain levels such as 20 dB for best noise performance, which definitely isn't right. Here's what I posted back then:

> [T]he topic from about 24:00 to about 30:00 in the recorded talk is dynamic range, which takes into account both the noise floor and the maximum SPL of the signal chain. He's very concerned to compare apples with apples: the digital microphone with the analog microphone PLUS the preamp that you have to use with it [whether standalone or built into a mixer or recorder].

> As he says (ca. 26:30), the CMD 42 isn't limited by having to pump out high voltages (more electrical power) at higher SPLs, so its maximum SPL is a few dB higher than that of the CMC 6. But when you bring an analog mike preamp into the picture (ca. 27:15), the clipping point of its output becomes a much more serious limiting factor when you get near the maximum SPL of the microphone. In the slide at the point that you mentioned, he's saying (around 28:20) that you would need to limit the gain on your preamp to about 15 - 20 dB in order to avoid this overload at the maximum SPL.

> He's definitely not saying that this is an optimal setting--on the contrary! His whole point is that analog preamps typically have lower input noise than the microphone's output noise only when set to higher gain levels than that, such as 30 - 35 dB. (This was shown in earlier slides, ca. 25:15 - 26:00.) Thus there exists no one gain setting for a typical analog preamp that both accommodates the maximum SPL of the microphone without clipping, and simultaneously offers the lowest noise for the quietest sounds that the microphone can pick up. If you need to record both at the very highest and the very lowest SPLs without touching any gain settings in between, the digital microphone offers a definite advantage as compared with the analog microphone--given that typical analog mike preamps can't put out 10, 20, 30 or more Volts (not that you really would want such levels to occur in practice).

> But then he goes on to say two things. (ca. 28:55) "With suitable operation of the preamp, I can obtain performance from the analog system that is exactly as good, or nearly as good, as that of the digital microphone. But I must operate it in a suitable way; I must really set exactly the gain level that suits my application exactly." Secondly, (ca. 29:50) combination analog mike preamps and A/D converters exist that use multiple analog gain stages and gain ranging--and he says that such equipment can produce results that are very nearly equivalent to digital microphones.

 

--best regards

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7 hours ago, DSatz said:

 

Thanks very much for the link and your commentary. Given what Wittek covers, I’m surprised at the small number of views and absence of any viewer comments. YouTube will auto-generate an English translation, and on a quick check it looks pretty fluid. The timestamped index below is in English in the YouTube description.

 

image.jpeg

 

 

 

 

 

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6 hours ago, DSatz said:

Um, no, I meant https://www.youtube.com/watch?v=2st7KzoEHlo starting at 24:01. This came up last August on an amateur audio forum that I sometimes participate in ("Tapers Section"), where someone had watched this video but perhaps didn't understand the German being spoken, and thought that Wittek was recommending to set analog preamps to low gain levels such as 20 dB for best noise performance, which definitely isn't right. Here's what I posted back then:

> [T]he topic from about 24:00 to about 30:00 in the recorded talk is dynamic range, which takes into account both the noise floor and the maximum SPL of the signal chain. He's very concerned to compare apples with apples: the digital microphone with the analog microphone PLUS the preamp that you have to use with it [whether standalone or built into a mixer or recorder].

> As he says (ca. 26:30), the CMD 42 isn't limited by having to pump out high voltages (more electrical power) at higher SPLs, so its maximum SPL is a few dB higher than that of the CMC 6. But when you bring an analog mike preamp into the picture (ca. 27:15), the clipping point of its output becomes a much more serious limiting factor when you get near the maximum SPL of the microphone. In the slide at the point that you mentioned, he's saying (around 28:20) that you would need to limit the gain on your preamp to about 15 - 20 dB in order to avoid this overload at the maximum SPL.

> He's definitely not saying that this is an optimal setting--on the contrary! His whole point is that analog preamps typically have lower input noise than the microphone's output noise only when set to higher gain levels than that, such as 30 - 35 dB. (This was shown in earlier slides, ca. 25:15 - 26:00.) Thus there exists no one gain setting for a typical analog preamp that both accommodates the maximum SPL of the microphone without clipping, and simultaneously offers the lowest noise for the quietest sounds that the microphone can pick up. If you need to record both at the very highest and the very lowest SPLs without touching any gain settings in between, the digital microphone offers a definite advantage as compared with the analog microphone--given that typical analog mike preamps can't put out 10, 20, 30 or more Volts (not that you really would want such levels to occur in practice).

> But then he goes on to say two things. (ca. 28:55) "With suitable operation of the preamp, I can obtain performance from the analog system that is exactly as good, or nearly as good, as that of the digital microphone. But I must operate it in a suitable way; I must really set exactly the gain level that suits my application exactly." Secondly, (ca. 29:50) combination analog mike preamps and A/D converters exist that use multiple analog gain stages and gain ranging--and he says that such equipment can produce results that are very nearly equivalent to digital microphones.

 

--best regards

 

Thank you for the translation! Appreciated a lot!

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Another advantage to digital mics is longer cable runs without signal degradation, although that is not all that relevant for us here. 


I found the combination of the Zax 743 with a SuperCMIT to be very noisy, so I am really curious how this will sound with the CMD42. 

On 3/29/2024 at 9:05 PM, The Documentary Sound Guy said:

Is there a more advanced interface for AES42 than what my Nova provides?  How are those advanced features accessed?  My understanding is AES42 is a spec for transferring digital audio (sometimes with self-power), not a control spec.  Schoeps has a list of AES42 interfaces and what features are included, and most of them do not provide more than power and sample rate conversion.

https://schoeps.de/fileadmin/user_upload/user_upload/Downloads/Kataloge_und_Broschueren/Prospektblaetter/AES_42_interfaces_for_Schoeps_CMD_42_and_SuperCMIT_-_Tabellenblatt1.pdf


It actually does include a control protocol, too. As Schoeps said, there is an LED to show the mic is on and I seem to remember that this LED on the Neumann digital mics could turn red when recording - but I may be terribly misremembering this. 
 

I do have the Neumann DMI-2 which was the control and power interface for Neumann digital mics. With a computer connected you could manipulate all kinds of settings, such as limiter, compressor, name and so on. This could be done live. I don’t know if newer versions of this could achieve any of this without the computer attached. 

On 3/30/2024 at 8:11 PM, VASI said:

 

The only two recorders which support Mode 1 & Mode 2, is Aaton Cantar X3 and Cantar Mini

What exactly would the be able to do in mode 2?

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I agree, my experience with the SuperCMIT is that it's definitely noisier than the regular CMIT through a TRX745 ... and also powered directly from the Nova.  I've attributed that to the internal pre-amp being lower quality than the one in my Nova, but maybe it also has to do with the lack of gain staging available?  SuperCMIT is tricky because the noise processing also affects the perception of the noise floor (less environmental noise due to cancelling means the electronic noise floor is more obvious).  But, I've found the unprocessed channel was also noisier than expected, so it's not just that.

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Before the topic changes completely, let me just chime in to agree with Constantin that AES42 is definitely more than just a passive interface for receiving digital audio signals. Unlike AES3 it has a control channel that runs from the interface to the microphone(s) (along the same set of wires, of course), and quite a few essential commands are predefined in the standard, such that all AES42-compatible microphones should implement them. Some other commands are "defined but optional." And there's also a range of command codes available for manufacturers to define for themselves however they want, so that unique features can be offered.

 

What you can do in Mode 2 that you can't do in Mode 1: [a] record synchronously with any given timing signals, such as a master clock, without using sampling rate converters [b] run multiple microphones without sampling rate converters. In Mode 1 each mike is independently self-clocking, and no two are ever exactly alike.

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On 4/2/2024 at 8:25 AM, DSatz said:

input noise than the microphone's output noise only when set to higher gain levels than that, such as 30 - 35 dB. (This was shown in earlier slides, ca. 25:15 - 26:00.) Thus there exists no one gain setting for a typical analog preamp that both accommodates the maximum SPL of the microphone without clipping, and simultaneously offers the lowest noise for the quietest sounds that the microphone can pick up. If you need to record both at the very highest and the very lowest SPLs without touching any gain settings in between, the digital microphone offers a definite advantage as compared with the analog microphone--given that typical analog mike preamps can't put out 10, 20, 30 or more Volts (not that you really would want such levels to occur in practice).


How come this limitation exists for analogue pre-amps but not for pre-amps in a digital context?  I understand that a digital signal doesn't use voltage in the same way as analogue (i.e. a digital signal doesn't use voltage to represent amplitude, and therefore doesn't need to vary as much), but presumably there still needs to be some circuitry that matches the output of the mic diaphragm to the input of the ADC.  Isn't there still an amplification stage to contend with before the signal hits the ADC, even if it's a fixed level gain stage rather than a variable pre-amp?  And, if that gain stage has to accommodate the same clipping level of the microphone, how come it doesn't suffer the same high noise floor as the pre-amp in a mixer console?

I believe what you are saying, but I can't follow the explanation.

8 hours ago, Constantin said:

It actually does include a control protocol, too. As Schoeps said, there is an LED to show the mic is on and I seem to remember that this LED on the Neumann digital mics could turn red when recording - but I may be terribly misremembering this. 


Interesting.  I wasn't aware of this.  I found your post and the document that VASI posted about his control protocol very enlightening, so thank you — I learned something.

That said ... AES42 is almost 25 years old now, and if the only devices (from Neumann, and perhaps Cantar?) that implemented this control protocol are now discontinued, I can't say my concerns about future compatibility have been much assuaged.  From what I read in the document VASI pointed to, it sounds like the control protocol is a different part of the spec than Mode 1 / Mode 2, so Schoeps database isn't as useful as it could be for identifying which devices support the control protocol and how much.  It looks like the RME DMC-842 might support it?

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Yes, but a FET impedance transformer stage is primarily a current amplifier; the voltage coming from the capsule is generally quite sufficient. Analog microphones have to drive loads as low as 600Ω sometimes; the IEC standard says 1 kΩ or greater, but some preamps don't maintain that at the frequency extremes--and you want to avoid a frequency-selective voltage divider effect, which necessitates almost a mini-power amplifier stage at the output of the mike.

 

But there's no such requirement if you're going from the impedance transformer directly into a converter; you can generally eliminate a circuit stage or two, and optimize your (internal) operating levels and impedances for best dynamic range. Neumann used a ganged, gain-ranging converter arrangement, and with some components that have been developed more recently, the input noise of the converter can be less of a problem to begin with. In the end the equivalent noise level of the combination can be within a dB or so of the corresponding analog microphone. Neumann achieved that in their AES42 microphones as well (they are certainly no slouches).

 

Schoeps had the CMD 42 under development well before Neumann / Sennheiser backed out. They felt that there is some range of customers who could be helped by this technology, and its development wasn't taking away too many resources from their other work, and was inherently interesting, so they continued. It was also affected by the pandemic and the owner's and managers' decision not to let people go even though new orders plummeted for a while (since then, the difference has been more than made up for).

 

They haven't gambled the whole farm on this one project, in other words. They'll do fine with their existing analog product line, which they've also been developing further. If manufacturers of mixers, recorders, and outboard gear choose now to offer more support for AES42, there'll be more of an "ecosystem"; if not, not. But there's no way that those other manufacturers could make digital microphones of a quality that people would want to use, so Schoeps has done their part--a big part in principle and potentially, in practice--and now we'll see.

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Also, Schoeps already had a digital preamp a while ago (I think simply called CMD) and discontinued it a shorter while ago. At the time they already said they wanted to develop a completely new digital preamp, but in any case, they surel weren’t starting from scratch. 
I can’t remember though, if this old digital preamp was AES42. I guess it must have been, because how else would it have been powered? 

Also, Schoeps already had a digital preamp a while ago (I think simply called CMD) and discontinued it a shorter while ago. At the time they already said they wanted to develop a completely new digital preamp, but in any case, they surel weren’t starting from scratch. 
I can’t remember though, if this old digital preamp was AES42. I guess it must have been, because how else would it have been powered? 
 

I am still unclear though of the advantage this digital body would bring to the movie world, especially if the 2 transmitters only really available compress the signal somewhat. At least I think Zaxcom does this. I find it hard to believe the quality improvement would be significant over analog transmitters, bit who knows. 
 

maybe it’s also time Lectro updated their DPR plugon to include AES42

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Thanks for the explanation DSatz!  I don't quite have the technical knowledge to fully understand it, but I got the gist I think.  How's this summary:  The electrical requirements of feeding an ADC are different from feeding a mixer input, so the pre-amp stage in a digital mic can be simpler and can be designed with a dynamic range that is greater than a traditional pre-amp.

I guess that puts the onus on the manufacturer to do a good job with that design (i.e., digital isn't automatically lower noise without a well-designed pre-amp stage), so hopefully Schoeps does a good job.  My only experience with AES42 is the SuperCMIT, and even the unprocessed channel is noticeably noisier than a regular CMIT ... but hopefully Schoeps has improved on that design in the CMD42.  I wonder how well it will cope with differences in sensitivity across their capsule lineup.

 

2 hours ago, Constantin said:

I am still unclear though of the advantage this digital body would bring to the movie world, especially if the 2 transmitters only really available compress the signal somewhat. At least I think Zaxcom does this. I find it hard to believe the quality improvement would be significant over analog transmitters, bit who knows. 


Me too.  But, it doesn't have to be for us.  I'm fairly certain you are right that both the TRX743/5 and the A20-Mini use compression to squeeze a digital signal into the available bandwidth; I don't see how they could not use it given the available bandwidth.  That said, my subjective impression from using the TRX745 is that it does sound noticeably (if subtly) cleaner than my Lectro HMa, and I have yet to identify any compression artifacts (it's still relatively new kit for me, and I still use wired boom more often than a plug-on).  It's not like the analogue transmitters don't have their own version of compression (i.e. a compander circuit).  The biggest differences I notice are a lower noise floor, and a more transparent limiter / compressor in the TRX745.

One issue I have with the TRX745 and the SuperCMIT specifically is the TRX introduces a small amount of RF interference to the noise floor ... there's a subtle 2K tone that shows up in the noise floor that isn't present when hard-wired.  In most practical scenarios, the ambient noise is enough to cover it, but it's a consideration for very quiet scenes.

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Constantin, the earlier Schoeps digital mike amp--introduced nearly twenty years ago--was the CMD 2. It, too, was an AES42 device, but it supported only mode 1, in which the microphone is self-clocking, which means that you can't sync your recording to a camera or house clock, or run multiple microphones, unless your recorder has sampling rate conversion built in.

 

The CMD 42 is indeed a complete redesign--as it should be, since the components available for a project like this are worlds better than they were twenty or even ten years ago.

 

--I need to disclose occasionally that I've done translating and editorial consulting for Schoeps for many years, and I'm subject to the human tendency toward bias. (Also equalization.)

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