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Schoeps Super CMIT experience?


Reinout Weebers

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The noise floor thing...... The Super CMIT seems to be a noisy mic. It is designed to help reduce off axis sounds, and it does this quite well. The implication in this is that the mic will be used in places where there is a bit of off axis, ie background, noise. My experience with Super CMIT was that in quiet places (studios, when the scene is quiet) and you have to wind the gain up, it is simply noisy. I spoke to Helmut from Schoeps at an IBC show a few years ago and he suggested that I roll off some HF above approx 8kHz. I have done this since and it works very well, but it doesnt sit so comfortably with my head - why am I tweaking the EQ for a mic that costs a good few grand because it is hissy!!!!

 

Kindest,

 

Simon B

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Hi Bash,

 

I totally understand you, esp. for that much cash. But the CMIT has also a bit more selfnoise than an MKH 416 for example.

Outside I would say that in most cases city ambience covers the selfnoise if not in remote nature (Thats where my MKH 70 shines with 5dbA on nature sounds). 

Selfnoise to me is much more obvious on my Sennheiser HD-25 compared to my Speakers.

 

So what do you use as your main shotgun?

 

Specs say:

 
MKH 8060                        11 dbA

KMR 81i                            12 dbA

MKH 416                          13 dbA

Super CMIT Channel 1   14dbA 

Super CMIT Channel 2   16 dbA

CMIT                                 14 dbA

CMC MK 41                     15 dbA

4017b                               13-15 dbA

CS 3                                  15 dbA

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So in mod 2 the mic is able to (word clock) slave to the recorder/amp.

And because I'm using the DA42 (mod 1 amp) for now, the mic is in free run and has to be re sampled by the SRC on the DA42 or my 788T.

Sounds logically, thanks!

Hearing is easy, listening is a craft.

If you use a 788T you don't need the DA42. The 788 has a AES42 input and it can in fact lock itself to the mic. However, afaik, it doesn't have remote control capabilities
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No remote control for Super CMIT has ever appeared, but for fast moving applications it would be very useful where the mic is in a full windshield.

I've a suspicion that it cannot be remote controlled or possibly could but only with new firmware. I've used it with a 788 and a Nomad, but although the 788 had a firmware update that enabled limiters on digital inputs the Nomad does not. 

I use Super CMIT with a DA42. Its performance is very often exceptional, even without full digital signal chain. I can live with some noise, for the focus and reverb suppression it can achieve.

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I tried one out, and my conclusion was as follows:

It's an amazing piece of technology, and effectively does in the field what we've all come to know as noise cancelling.

For me, I decided I didn't want to do in the field what Izotope can do better in post production.

Izotope cannot do better in post because it doesn't have the same phase information to work with, which has effectively been stripped out by mono recording.

Perhaps think of it as the Super CMIT can work in 3D space whereas Izotope can only work in 2D, and although Izotope may be able to make a good stab at noise reduction, it will not be the same.

An artist can work directly from nature or from a photo perhaps, but nothing like being there on the day. :)

That's what's so clever about the Super CMIT from a high class and innovative manufacturer, who also make other clever tools available like the double MS to surround decoder available for free, for example.

Schoeps put their profound knowledge of microphones and sound, as we all know, to very good use.

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Also maybe noise cancellation in headphones for example is different to off axis cancellation in microphones. In headphones its subtractive like a notch filter, what the Super CMIT is doing is much more sophisticated and doesn't reduce particular frequencies to the detriment of what's on axis. Is that correct?

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I was under the impression that the SuperCMIT was a mod 2 mic, so that cleared up some things for me.

 

Schoeps website:
The SuperCMIT 2 U is a digital microphone. Its output signal format is AES42, Mode 1. This means that it runs on its own clock (48 kHz) and must be driven by an AES42 input with a sample rate converter (SRC).

 

I once read an article from John Willett (are you on here?) that explained the digital mic. Read it again. Was helpfull ;-)

http://www.taperssection.com/reference/pdf/AES%20-%20Digital%20Microphones%20-%20AES42%20and%20all%20that.pdf

 

Reinout

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It's true, they are putting a lot of emphasis on the src, but I don't see why a recorder like the 788T shouldn't be able to lock its digital clock to to the incoming AES signal. It does that with my Neumann digital mics, although Neumann say the same as Schoeps and I can't say for sure if the src is disabled or not

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  • 5 months later...

 

if your mic is newer than September 2010, you can add 30dB to the digital output of the mic. You can do this now by pressing twice each of the three buttons on the mic. However, this will not improve your snr as it all happens in the digital domain

Thanks so much for that (AFAIK unpublished) pointer, Constantin! So glad I dug through this thread, and found this nugget of information - I'm demo-ing a SuperCMIT for an upcoming job, and was baffled because I cranked up both the trim and the fader on my 664 just to hear anything on the track. I simply thought something was wrong with this particular mic…

Cheers,

BK

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It's true, they are putting a lot of emphasis on the src, but I don't see why a recorder like the 788T shouldn't be able to lock its digital clock to to the incoming AES signal. It does that with my Neumann digital mics, although Neumann say the same as Schoeps and I can't say for sure if the src is disabled or not

The Mode 1 is not clocked. The recorder must use SRC to use the signal with its internal sync.

"Mode-1 is AES42 in its basic form.  Each microphone is free-running from its own internal clock – so, if you want to use several AES42 microphones together, they will have to go through a sample-rate converter to clock them. 

 Mode-2 allows the microphones to be clocked from the receiving equipment – the clock signal is sent to the microphones as part of the data stream.  Advantages include: no SRC and a constant phase relationship (close to 0°) between different mics, independent of cable length or other influences.  Mode-2 devices can also be run as Mode-1 when being used in a system that also contains microphones that work Mode-1 only.  "

 

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The Mode 1 is not clocked. The recorder must use SRC to use the signal with its internal sync.

"Mode-1 is AES42 in its basic form.  Each microphone is free-running from its own internal clock – so, if you want to use several AES42 microphones together, they will have to go through a sample-rate converter to clock them. 

 Mode-2 allows the microphones to be clocked from the receiving equipment – the clock signal is sent to the microphones as part of the data stream.  Advantages include: no SRC and a constant phase relationship (close to 0°) between different mics, independent of cable length or other influences.  Mode-2 devices can also be run as Mode-1 when being used in a system that also contains microphones that work Mode-1 only.  "

 

yes yes, but as above: the mic is running from its own internal clock. So it is clocked. Why can't my recorder lock to it if I am using the SuperCMIT as my only digital mic?

or is the internal clock so unstable that my recorder would suffer? But that wouldn't be good for the mic either

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  • 8 years later...

I just acquired a SuperCMIT and took it out in the field for some birdsong recording this morning.  It was a very unusual experience.  I've never used a mic like this.  It took some getting used to.  A VERY different tool than my mid-side MKH60/MKH30 setup, which I had side-by-side.  In the end, it's a great tool for zeroing in on specific animals, which was great.  It's so precise, I was able to record bird footsteps, which I've never picked up in a recording before.  I was able to use it in an urban environment and filter out a great deal of the hum and rumble that ruins a "wildlife" recording in that context.

I wouldn't use it for ambience, which I guess is understandable given how much it filters out.  Not the right tool for that.

I didn't find it very transparent, even in the lighter of the two noise reduction settings.  Off-axis sounds sounded phasey and bizarre (footsteps on gravel were particularly offensive), and even when that wasn't bothering me, the complete lack of low-end made off-axis sounds very strange.  But a powerful tool that is capable of things I haven't been able to do before.

So much for the review.

The real reason I'm posting is because there was a distinct tone in both channels (with NR and direct from the CMIT) at exactly 1,500Hz (and all harmonics).  With a noisy background, it was inaudible, but it was loud enough to ruin a quiet recording.  In the sample recording I've uploaded, it floats about 10dB above the ambient sound, so it's well above the noise floor of the mic.

Is this normal?  I'm inclined to say the mic needs service (which is understandable ... I bought it used), but I'd like to hear from other owners whether this should be expected.  The attached recording demonstrates the issue.

If it's not normal, is it possible I'm hearing RF interference?  Could the be an artifact of the recorder (Zaxcom Nova2)?  I've not played with any other digital mics, so I'm in somewhat new territory in terms of knowing what could cause this ... I'm inclined to say it's happening in the mic itself, before conversion to digital, or perhaps as a side effect.

In any case, if this is just how the mic is, I'm not happy and I'll resell it, but I'd be shocked if it is given Schoeps' reputation and the cost of the mic.  If it's not normal I want to fix it.

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One thing to bear in mind about the SuperCMIT, to my understanding, it was originally designed as a 'Pitch side' shotgun style mic to heavily reject the crowd noise. I believe it was for a specific large stadium sporting event, but cannot remember details.

I humbly suggest that the recording of nature ambiences did not see a mention on their design brief. Heck, I don't think Drama Dialogue recording would have been at the time either! The point being is that I'm sure a lot of compromises were taken to achieve the desired results, one of which I'm sure was 'self noise' (noise floor).

I've used a SuperCMIT for a few years (a few years back now) for normal PSC duties, and it is one noisy mic! Not suitable for sit down interviews etc. but on a few occasions, it was the only tool for a noisy location (ext. mostly), for PSC and a drama or two in my case.

Right tool for the job? Depends on the job.

W

 

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It's definitely an unusual tool!  The product page has demo recordings of a football bounce being captured in a stadium, so that use-case makes sense.  I believe I've also seen them on screen for tennis matches to capture the tennis ball bounce and other court noise (athletes breathing etc).  The same page also gives a demo of an interview next to running water, so I don't think it's entirely fair to say interviews aren't an intended use case, though I take your point that it's mainly good for outdoor scenarios where the noise reduction is necessary.  This is the primary use-case I had in mind when buying it, and I guess it does work for that.

 

That said, given the price and the pedigree, I'm quite surprised that more care wasn't taken with anticipating other applications.  I have trouble believing that a 1.5kHz noise spike at least 10dB above the rest of the noise floor is the result of a design compromise.  That suggests to me that something in the internal pre-amp or ADC stage is ringing (since the tone appears in the unprocessed channel as well).  I would believe a compromise in the noise reduction algorithm, but the capsule of the CMIT was already a known (and good) design, and I can't quite wrap my head around why they would feed a noise reduction algorithm a deliberately noisy signal ... especially since the noise reduction makes the pure tone more audible.  And if it is somehow an intentional design compromise, why couldn't they just notch filter it out at the end?

I guess there's no point speculating though.  It is what it is.  I'm just disappointed, because, other than the pure tone, it *does* seem like a good tool for zeroing in on quiet sounds in a wild environment.  I hadn't heard wildlife in quite that way before.

Makes me wish it was possible to control the internal pre-amp gain ... I wonder how much quieter it could be in a scenario where it could be gain-staged for low noise?

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A tone "..at exactly 1,500Hz (and all harmonics).." you say, (Doc Sound Guy). Hmm, I just did a test and didn't hear that. I used my SuperCMIT in AES (digital) mode (both processed and unprocessed audio thro' the 'double' AES digital output) and then tested it in purely analog output mode, and in analog I compared it with a 416. I used 12v battery power from a large powerbank battery ..as I usually do.. to run the SCMIT, and recorded with an internal-battery 744T. I stood in a large first floor room to record just my voice from about 6' away, then I opened the balcony doors 6' behind the mic(s) to capture sound, too, from out on the street outside.

 

At first I heard next to nothing from the SCMIT, but then, of course - silly me! - I'd forgotten to press 'boost' on the SCMIT (double-press on each of its three buttons) and audio came roaring into my cans (Sony 7506, or whatever they're called)!

 

The SCMIT in (stronger) Preset 2 mode sounded less 'boxy' than it does in a small room, and was reasonably usable, but without much bass (no EQ was used). My voice was way louder than the background outdoor sounds. Using (weaker rear cut) Preset 1, traffic and birdsong sounded louder, a little more bass was apparent, but my voice was almost disappearing into the background sound. The unprocessed audio from the 2nd AES channel had somewhat louder background audio, and a little more bass. Interestingly, could find hardly any 'out-of-phase' delay between processed and unprocessed audio.

 

Switching to completely analog output, everything was pretty much as above, but I plugged the 416 into Mic Input 2: the 416 gave much more bass, but my voice was completely swamped by the outdoor sounds coming from behind the mics.

 

When I started the recordings, (in digital mode), I heard some hum or faint buzz, but realised that was the sound of the 744's hard disc whizzing, as I had the recorder and mics resting on the same table: I lifted the recorder off the table and put it on a cushion, and the faint buzz disappeared.

 

Playing the recordings I could hear a very faint 50Hz(?) buzz or hum ..but realised that this had been from the fan in a central heating boiler about 50' behind me(!) ..but no 1,500Hz buzz at all. They were all very clear recordings, with no extraneous audio except for that faint distant boiler fan hum/buzz.

 

The SCMIT certainly cuts away distracting background (e.g; street) noise, but let a little birdsong through (sounded quite nice), and though I preferred the 'tone' (richness or better bass) of the 416, my voice was almost incoherent against the background 'ambient' noise.

 

But I heard no extra hum, buzz or "1,500Hz (and all harmonics)" thro' the SCMIT at all ..and never have. But maybe my hearing's defective.

 

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Thanks.  That gives me hope that maybe a trip to Schoeps can help.  I sent them a message at the beginning of the week asking, and I haven't had a response yet.

Are you able to hear the 1.5kHz tone in the recording I posted?  It's quite obvious when you look for it, and a spectrogram shows it clearly (this is how I know it's exactly 1.5kHz and all the harmonics).  I would emphasize that it's honestly not that loud ... it disappears completely in noisy environment, so it's not a problem all the time, but my birdsong environment was quiet and the problem became quiet obvious.

Can you explain more about "analogue output mode"?  I didn't think it was possible to get an analogue output.  Do you mean the unprocessed channel?

Oh, maybe you are taking analogue from an external power supply (a MiniDA42 perhaps)?  Is that what you mean?

If that's the case, maybe it's the AES supply in my Nova that is cause issues?  I'm getting an AES cone for my TRX745, so I should have an alternate power supply to test with in a couple weeks.

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I'll have a closer listen tomorrow to try and hear the 1.5kHz tone (it's bedtime here in the UK.)

 

By "analogue output mode" I mean that the SCMIT can deliver (A) a 2-channel purely digital output down its single AES digital XLR cable from its little box (my little box is the Mini-DA42 with its three different output cables, not the  PSD2U box) ..OR (B) that Mini-DA42 box can deliver two purely analog  outputs (the output of its digital processing within the mic) which are compatible with any ordinary non-digital, analog Mic IN sockets on any recorder at all ..e.g; a Zoom recorder, or an old tape machine, or ..well, anything!  (The two analog  outputs of the Mini-DA42 box, which are output down two separate cables, are (1) the digitally-processed audio as selected on the mic with Preset 1 or Preset 2 (reducing rear pick-up) which is converted from digital to analog via the little box, and (2) also unprocessed audio, just like the sound from an ordinary non-Super CMIT.)

 

(BOTH the digitally-processed audio AND the UNprocessed audio come down the single digital AES-compatible output cable from the little box if you choose to plug the AES-compatible cable into a digital AES-compatible socket on a recorder which has a digital AES socket, e.g; a 'PortaDat' or, in this case, a 744T. My IV-S doesn't have a digital input, so I use either - or both of - the analog output(s) instead [which are two separate cables out of the mini-box] to get processed  sound in through one mic connection, and (maybe I prefer it unprocessed) unprocessed audio in through a second mic connection. It's a European IV-S, so it doesn't have input sockets ..it has input plugs! ..Weird, eh?)

 

In summary: the SCMIT can give TWO outputs (processed and non-processed; meaning 'raw', like an ordinary short shotgun) which BOTH come down the one single digital 'AES' output XLR cable, thus providing two alternative sounds into the recorder, OR the two analog cables from the mini-box provide the same TWO (processed and also un-processed) audio outputs down two analog XLRs for connecting into any old non-AES (that's non-digital) mic inputs of any recorder which does not have a digital (AES) input. The digital output(s) and the analog output(s) - [converted from the SCMIT's digital innards] - sound exactly the same ..to me, anyway.

 

So TWO kinds of audio (both processed and un-processed) can be fed down a single cable into any recorder which has an 'AES/EBU' digital input, but the same TWO kinds of audio can also be fed into the mic sockets of any device which does NOT have a digital 'AES/EBU' input.

 

(Gotta go to bed now.. G'nite.)

 

P.S:  "..my birdsong environment was quiet and the problem became quite obvious.." ..and was it more or less  obvious when you boosted the SCMIT's output (two presses on each of its three buttons)? ..Did the 1500Hz tone get boosted, too ..or was it then drowned out by much louder birdsong? 

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Thanks for explaining.  I don't have the Mini DA42, so I don't have any form of analogue output ... I'm just plugged directly into my Nova2, which provides the power and accepts both channels directly in the recorder.

You make a good point about trying the "boost" mode ... I wasn't using it, and I haven't actually tried it yet.  I had assumed it wouldn't do anything because the boost happens in the digital domain, but I don't think that assumption is valid.  So thanks, you've given me something to try that could help.

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Mmm ..the recording level is extremely low, so I'd use the 'boost' in future.

 

I listened to your recording - and downloaded it and opened it in various audio players; I often use the quick'n'easy 'Audacity' - and I hear NO 1500Hz tone anywhere in the recording (listening through TiTum, Sony 7506, Senal SMH-100 and Grado SR325 cans).

 

I do hear lots of low level general normal outdoor background rumble and hiss, but I don't hear any 1.5kHz tone "10dB above the ambient sound". Nor does such a tone appear in Audacity's waveform display, as far as I can see ..it's just random background hiss when I've amplified it 16x, 20x or more .

 

Maybe it's coming from the kit which you're using to play  the file(s), or maybe you're playing them in the vicinity of something which is generating 1.5kHz, but the files themselves seem, to me, perfectly clean (apart from the slight background hiss). I'm sure it's not the mic generating it.

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