Topic: digital mics (portable AES 42, schoeps, neumann)

[jerryfreak]

im sure you all have heard about these by now. from what i have read, the neumann mics can output either aes 42 or aes/ebu (tho im not sure of the latter without the use of the latter without neumann's AC-powered D-01), and the schoeps CMD series bodies apparently only work with AES42

it appears the AES 42 standard requires digital signal, some phantom powering, and some remote control signals

some Q's for discussion:

1) looks like this standard isnt publically available: http://store.ihs.com/specsstore/controller?event=LINK_DOCDETAILS&mid=W097&getCurVer=false&docId=ZZEFBCAAAAAAAAAA&mid=W097
does anyone here know any details of it? is it within the scope of the peeps on this list to build a portable interface?

2) i would think it would be ideal for an 'all in one' box, similar to the nbox, but with spdif out.something with a master clock, proper control of mic sample rate, and an aes42>12s>spdif circuit.

3) can you invision a world where bit buckets evolve until your rig is 'schoeps mk4>custom cable>microtrack at 24/192'

I'm getting that 'too good to be true' feeling, tho.....

[Alexandru Petrescu]

[...]
3) can you envision a world where bit buckets evolve until your rig is 'schoeps mk4>custom cable>microtrack at 24/192'

Not visionary enough... I'd add bidirectional wireless (send voice to  studio and receive config data) to the picture; also micro-mechanically switching polar patterns; all running on a dime-sized battery.

Alex

[jerryfreak]

well you got me beat there!

i guess beyond that were recording what we actually hear to a chip implanted in our brain

FYI, i contacted neumann and schoeps, and it is possible to run these without a proper AES42 input.

more later

[...]
3) can you envision a world where bit buckets evolve until your rig is 'schoeps mk4>custom cable>microtrack at 24/192'

Not visionary enough... I'd add bidirectional wireless (send voice to  studio and receive config data) to the picture; also micro-mechanically switching polar patterns; all running on a dime-sized battery.

Alex

[Alexandru Petrescu]

:-) hehe right yes, I think envisioning a world with early A/Ds in portable mics is not very far-fetched, as witnessed by the USB microphones.  Digital is just another new dimension in the all-known audio trade-offs space; eg if a spdif interface must be small lowpower it will be 16bit/44khz making its edging 24bit recorder and 100KHz capsule useless... maybe R09 moving from 44khz to 96khz and losing its digital output confirms this speculation too :-)

I looked closer at the Neumann descriptions ('kmd' is that?) and the one obvious impediment for portable recording seemed to be the need of supplementary power for the digital interface... the other being the supplementary size of the spdif converter.

I think only Neumann could feed a 'bit-bucket' spdif like MicroTrack's whereas Schoeps ('cmd'?) wouldn't support spdif.

For the AES standard being open: they'll surely say it's open, all standards are so, which wouldn't stop its textual description from being sold, which wouldn't stop a motivated implementer or her/his employer to buy it considering the amount of money s/he's going to make by selling devices...

Yes, please keep us posted about the feedback from neumann and schoeps about running these.

well you got me beat there!

i guess beyond that were recording what we actually hear to a chip implanted in our brain

FYI, i contacted neumann and schoeps, and it is possible to run these without a proper AES42 input.

more later

[...]
3) can you envision a world where bit buckets evolve until your rig is 'schoeps mk4>custom cable>microtrack at 24/192'

Not visionary enough... I'd add bidirectional wireless (send voice to  studio and receive config data) to the picture; also micro-mechanically switching polar patterns; all running on a dime-sized battery.

Alex

[jerryfreak]

they both said the neumann adapter shown here:

http://www.neumann.com/download.php?download=copi0098.PDF

would work to power both the neumann and schoeps fine,

the trick being each one puts out a spdif mono signal, so you'd need two spdif recorders and some post-work

also, you'd need access to somebody with an AES42 compliant console to set the sample rate initially, then it would remain at that setting with the adapter until you changed it with a AES42 console.

I could live with the mics set to 48 or 96k relatively permanently.

the big question is there any advantage over a standard cmc6 for our application?

i would think that the self-noise of the capsule would be the limiting factor. you may buy some range, but how much?

:-) hehe right yes, I think envisioning a world with early A/Ds in portable mics is not very far-fetched, as witnessed by the USB microphones.  Digital is just another new dimension in the all-known audio trade-offs space; eg if a spdif interface must be small lowpower it will be 16bit/44khz making its edging 24bit recorder and 100KHz capsule useless... maybe R09 moving from 44khz to 96khz and losing its digital output confirms this speculation too :-)

I looked closer at the Neumann descriptions ('kmd' is that?) and the one obvious impediment for portable recording seemed to be the need of supplementary power for the digital interface... the other being the supplementary size of the spdif converter.

I think only Neumann could feed a 'bit-bucket' spdif like MicroTrack's whereas Schoeps ('cmd'?) wouldn't support spdif.

For the AES standard being open: they'll surely say it's open, all standards are so, which wouldn't stop its textual description from being sold, which wouldn't stop a motivated implementer or her/his employer to buy it considering the amount of money s/he's going to make by selling devices...

Yes, please keep us posted about the feedback from neumann and schoeps about running these.

well you got me beat there!

i guess beyond that were recording what we actually hear to a chip implanted in our brain

FYI, i contacted neumann and schoeps, and it is possible to run these without a proper AES42 input.

more later

[...]
3) can you envision a world where bit buckets evolve until your rig is 'schoeps mk4>custom cable>microtrack at 24/192'

Not visionary enough... I'd add bidirectional wireless (send voice to  studio and receive config data) to the picture; also micro-mechanically switching polar patterns; all running on a dime-sized battery.

Alex

[jerryfreak]

btw, this is possible right now:

MK4>CMD2>KMD adapter>2x microtrack @24/96 > soundforge (time correction, stereo mix, fades and edits) >CDWAV > FLAC

[DSatz]

The AES42 standard has created a bit of an odd situation. As you can see from Neumann's product lineup, it isn't hard to power one microphone at a time and derive either an AES/EBU or S/P-DIF signal from it. That's great for the project studio people who only "track" with one microphone at a time.

But for those of us who record in stereo using 2, 3 or 4 microphones at once, there's a bit of a problem: Each digital microphone contains its own clock circuitry, so no two are exaaaaaaaactly alike. Thus when more than one microphone at a time is being used, one of two things must occur:

(1) The signals from the microphones must go through a process of asynchonous sample rate conversion so that the signals they deliver can be recorded synchronously, or

(2) The clocks in the microphones have to be nudged into conforming to an external master clock.

The AES-42 standard has an extremely ingenious way for approach (2) to work. The interface which powers the microphones observes their exact data rate, and advises them (via a flag in the bitstream) to slow down or speed up until everything is properly in synch. In my opinion that is distinctly preferable to any asynchronous sample rate conversion.

Unfortunately, however, the only free-standing implementation of this approach that I know of is in Neumann's DMI-2 interface, which currently lists for $1,418.00 in the United States. I assume that the powering and synchronization could be implemented for less than that, but probably not very easily.

A courtesy PDF copy of the standards document can be downloaded at no charge from the AES' Web site. See http://www.aes.org/publications/standards/ .

By the way, as someone else mentioned previously, Schoeps' digital microphones work just fine with Neumann's powering adapters--one advantage of having such a standard, and of manufacturers who treat such standards with appropriate respect. Schoeps doesn't offer any powering devices for digital microphones; they anticipate that this facility will be built into preamps, mixers and recorders in the not-too-distant future.

I personally am in no great hurry to convert to this approach, since its advantages in my type of application are so minor compared to the costs. If the advantages increase or the costs decrease, that will tilt things a little differently. For me, for now, I don't find that the analog interface limits my ability to get a good recording when my mikes are in the right place at the right time.

--best regards

[jerryfreak]

listen here mr rational advice guy, if we wanted rational advice instead of dreaming and slutting it up, we know where your trashcan is! 

j/k, thanks as always for your input

my own feeling is hte timing issue would be minimal between two mics.

phasing and timing issues are more prevalent with two stereo sources mixed together, but for just a L and R channel, there is inherent phasing and timing issues anyway, and i think you could make an assumption that the clocks may be different, but both consistent in timing to themselves. you would correct the timing by a simple software reclocking of the whole track from a start and end point, and that would work 99% of the time.



The AES-42 standard has an extremely ingenious way for approach (2) to work. The interface which powers the microphones observes their exact data rate, and advises them (via a flag in the bitstream) to slow down or speed up until everything is properly in synch. In my opinion that is distinctly preferable to any asynchronous sample rate conversion.

Unfortunately, however, the only free-standing implementation of this approach that I know of is in Neumann's DMI-2 interface, which currently lists for $1,418.00 in the United States. I assume that the powering and synchronization could be implemented for less than that, but probably not very easily.


yes but realistically in 5 years we could see this type of logic on a single chip that could easily be integrated into a small digital phantom power/spdif data/clock synching circuit design (or perhaps even a chip that did all of those, with additional software dsp's, etc).


future looks bright for the geeks. and props to the old schoolers in germany who are still pwning the worlds faces with their microphone technology to this day.

[DSatz]

jerryfreak, OK on the sluttitude, but the problem is that the S/P-DIF or AES/EBU outputs of Neumann's simple powering solutions are all single-channel. For stereo recording you can't just plug two of them in side by side because of the timing issues. It's not just the tiny divergence among different samples of the microphones--it's how are you going to interleave the data from two microphones (it has to go exactly in order, left/right/left/right, with the proper sync bits and protocol bits in the exact right places), when each microphone is running on its own independent clock, and there's no central device that's bringing the two signals into a common feed?

In a two-channel S/P-DIF or AES/EBU signal, the sample values are interleaved left/right/left/right etc.--your interface or recorder then syncs to that signal, which is "self-clocking" (i.e. the equipment receiving the signal can derive its own master clock from it). If you feed in two independent signals with different clocks and random, uncoordinated relative timing (i.e. when does each microphone start sending the bits for each new sample?), the recorder or interface can't sync to them both at the same time unless it does the thing I called (1) in my message above. With each microphone delivering its own sample values at randomly (un)related points in time, you can't just combine those two outputs into one data stream in any simple way.

Am I making myself clear here? There's a fundamental issue that won't go away no matter how you slice it.

--best regards

[John Willett]

I have the Neumann KM-D series and use them in anger.

There are *two* devices that I know of that take AES42 microphones - the Neumann DMI-2 and the new 8-channel RME unit.

Schoeps units always run asynchronously and need a sample-rate converter.

The Neumann units can run asynchronously or synchronously, clocked by the DMI-2 or the RME.  Same with the new Sennheiser AES42 unit for the MKH 8000 series (due later this year) - but the Sennheiser can run two capsules.

If you want to run the Neumann in stereo with the adaptor units you will need a sample-rate converter to sync. them.

I think DSatz has already said most of this already (but he missed the availability of the RME unit I think).

Taking everything into account the AES42 microphones are not expensive when you consider that you don't need a mic. pre. and they also have built-in limiters (certainly the Neumann and Sennheiser do, I don't know about the Schoeps in this respect) to prevent clipping.

Basically AES42 is an AES3 signal together with a 10V / 250mA phantom power and data stream both ways.

[Alexandru Petrescu]

Taking everything into account the AES42 microphones are not expensive when you consider that you don't need a mic. pre. and they also have built-in limiters (certainly the Neumann and Sennheiser do, I don't know about the Schoeps in this respect) to prevent clipping.

Sounds tempting.

Factoring out the sync issues I don't quite understand, and in the advantageous absence of a larger analog preamp - what are the digital A/D inconvenients of the digital mics compared to using a larger external A/D?  For example, maybe 1bit AD is more flexible than eg Schoeps CMD2U's builtin 24/192k?

Just some thoughts, otherwise yes, looks tempting, a setting where analog noise is no longer an issue...

Alex

[DSatz]

Alexandru, it is simply not true that "analog noise is no longer an issue." A digital microphone (of the type we are talking about) is nothing but a combination of an analog capsule, an analog FET front end stage (and those are the two main noise sources in any condenser microphone already), followed by an A/D converter.

It is like the difference between a separate tuner, preamplifier and power amplifier on the one hand, and an integrated "receiver" on the other. The only noise which is reduced in a receiver is the noise which comes from connecting several components which might not be ideally suited to one another.

If you compare the equivalent noise level of any available digital microphone which has an analog counterpart, the equivalent noise level of the digital version is always greater--as it must be. You can plainly see this in the specifications of both Neumann and Schoeps, for example.

Of course, the proper comparison would be with the equivalent noise of the analog microphone plus an preamp and A/D converter--but there are many possible choices of preamp and converter, and no standard form of specification exists for such a combination, so this gets into an area of some debate.

--best regards

[John Willett]

The AES42 standard dictates a 24 bot output from the mic.

The better noise figures from digital come from the fact that you don't have to back off the mic. pre. and A/D to allow for headroom - also the digital mic. can have a built-in digital limiter to prevent clipping.

[ghellquist]

Now, what I really would love to have is digital mics transmitting wireless to my recorder. Lately I have started to hate cables more and more.

The digital mics seems to give a really good amplification and AD. It can perhaps be bettered slightly with other preamps + converters but the difference is probably tiny.

It would need resampling at the receiving end but that probably makes only tiny changes in the sound. Now, think of something the size of a normal small condenser mic (say like a MKH 20), with built in digital converter and transmitter. Built in battery running, say, 10 hours. 8 of these mics and I would be able to do most of my classical recordings without cables focusing on getting mic placement right instead. Now, that is something to dream of (and I believe it is not really that far away technically).

Gunnar

[John Willett]

Now, what I really would love to have is digital mics transmitting wireless to my recorder. Lately I have started to hate cables more and more.

The digital mics seems to give a really good amplification and AD. It can perhaps be bettered slightly with other preamps + converters but the difference is probably tiny.

It would need resampling at the receiving end but that probably makes only tiny changes in the sound. Now, think of something the size of a normal small condenser mic (say like a MKH 20), with built in digital converter and transmitter. Built in battery running, say, 10 hours. 8 of these mics and I would be able to do most of my classical recordings without cables focusing on getting mic placement right instead. Now, that is something to dream of (and I believe it is not really that far away technically).

Not technically possible at the moment.

Great idea, though.

A normal phantom mic. takes 2mA - an AES42 digital mic. takes 250mA. + digital trandmitter..............

Battery life of about 5-minutes I think. 

Hopefully one day..................................................