Digital microphones

[BrianHanke]

Well, it's time for my semiannual inquiry about digital mics. I'm on the verge of trading in my Neumann KM131s for a pair KM Ds. I've long found the idea of digital mics to be highly appealing and I've been looking for an excuse to make the switch.

However, I don't want to go to the expense of purchasing the Neumann DMI-2, plus a recorder or computer interface with AES inputs. My plan is to get a pair of KM Ds with S/PDIF connection kits (preset at the factory to 96 kHz sample rate) and hook them into two daisy-chained TC Electronic Konnekt 8 interfaces. This seems like an excellent and cost-effective solution to me.

The only problem? Nobody I've talked to has ever done this before. TC Electronic support has said they think it will work, and Neumann was cautiously optimistic. That sounds good, but I'm hoping to get a completely definitive response. I'd hate to spend a boatload of money only to find out I can’t record in stereo because of sample rate or sync problems. Has anyone here done this before? Any thoughts or opinions? Many thanks in advance!

[mpdonahue]

My take on this is that it is a solution in search of a problem.
We've looked into the various AES41 hardware options and concluded that the sample rate conversion, cable length restrictions and interfacing issues far outweigh any benefit gained from the conversion at the microphone. (I'm sure that others will disagree, as always YMMV)
Also, digital conversion technology is steadily improving. From an investment standpoint, I find purchasing a microphone with a built in obsolescence a little troubling. Just like most purchases of digital gear, as the technology improves, the value of old digital goes into the toilet. (Let me tell you about the 3324 I tried to give away... I can't even take it to the dump and throw it away because of the lead in the Solder)

All the best,
-mark

[d_fu]

Originally Posted by BrianHanke

However, I don't want to go to the expense of purchasing the Neumann DMI-2, plus a recorder or computer interface with AES inputs. My plan is to get a pair of KM Ds with S/PDIF connection kits (preset at the factory to 96 kHz sample rate) and hook them into two daisy-chained TC Electronic Konnekt 8 interfaces. This seems like an excellent and cost-effective solution to me.

But not a working one, methinks... I'm surprised that Neumann seemed to think it might work. If you feed two unsynchronized SPDIF signals into two separate audio interfaces, you will get clicks... Depending on the clock quality, they may not be frequent, but they will occur...

You would need some kind of device with Sample Rate Conversion that will accept unsynced SPDIF signals and convert them to e.g. ADAT.

Here's another alternative, but only for desktop PCs... Get the AES/EBU connection kits and the Marian Trace D4 SRC, a soundcard with onboard SRC...


As for Mark's comment about obsolescence, that's a point to consider, but I happily use ye olde Beyer MCD 100 digital mic from around 1996 (I've got three, in fact) with outdated converters and sample rate conversion in the special interface box, and I'm very satisfied with the results...

Daniel

[BrianHanke]

Thanks for your thoughts Daniel. The fact that there is so much disagreement about the feasibility of this makes me worry...

From what I've heard from Echo Audio and TC Electronic, daisy chaining two interfaces will allow the units to achieve clock synchronization. Two AudioFire 8s would apparently need to be synced via wordclock using a separate cable, but the Konnekt 8s sync via firewire.

Is this type of synchronization sufficient to eliminate clicks? TC Electronic also sells a dedicated sample rate converter (the Digital Konnekt X32), but if I'm going to spend that much money I might as well get the DMI-2.

Thanks also for reminding me about the Marian card. It looks like the price has come down, so that might be a good option.

Mark, I appreciate your insight, but I disagree a bit about the obsolescence factor. The Neumann mics offer sample rates up to 192 kHz and it's hard to imagine that even higher rates will become the norm any time soon. In my situation issues such as cable length restrictions also don't come into play.

Originally Posted by d_fu

But not a working one, methinks... I'm surprised that Neumann seemed to think it might work. If you feed two unsynchronized SPDIF signals into two separate audio interfaces, you will get clicks... Depending on the clock quality, they may not be frequent, but they will occur...

You would need some kind of device with Sample Rate Conversion that will accept unsynced SPDIF signals and convert them to e.g. ADAT.

Here's another alternative, but only for desktop PCs... Get the AES/EBU connection kits and the Marian Trace D4 SRC, a soundcard with onboard SRC...

Daniel

[d_fu]

Originally Posted by BrianHanke

From what I've heard from Echo Audio and TC Electronic, daisy chaining two interfaces will allow the units to achieve clock synchronization. (...) Is this type of synchronization sufficient to eliminate clicks?

No. It's not the audio interfaces, but the SPDIF connection kits that would need to be synchronized. If you have two free-floating, unsynced devices in a setup, you will have clicks (unless you have an SRC).

TC Electronic also sells a dedicated sample rate converter (the Digital Konnekt X32),

Interesting device, but certainly overkill...

The Neumann mics offer sample rates up to 192 kHz and it's hard to imagine that even higher rates will become the norm any time soon.

True, but progress in converter technology isn't only about higher sample rates, is it?

[Plush]

Sorry, but two digital mics plugged separately will not sync without a sample rate converter. It is a good idea to buy the Neumann DMI if you want to fulfill your plan.
YOur plan as described will not work--because you're not synchronizing the boxes, your goal is to sync the converters in the mics themselves---clock must come from the digital mic.

I think a digital mic experiment would be fun. I wonder if a difference could be heard?
(between a digital mic and the same mic plugged in to a neutral mic amp into a top a/d converter ? Methinks there would be no difference but I keep an open mind.

[BrianHanke]

I think I'm beginning to understand how this works.

The signals from the two mics will inevitably be slightly desynchronized. The problem comes when the master device (in my proposed case, one of the Konnekt 8s) polls both mics with reference to a single clock. There will be times when one mic is between samples and that's when a click will happen.

However, with a sample rate converter, the gaps between samples will be interpolated so that data can still be recorded even if the original signal is between samples. Am I on the right track here?

Originally Posted by d_fu

No. It's not the audio interfaces, but the SPDIF connection kits that would need to be synchronized. If you have two free-floating, unsynced devices in a setup, you will have clicks (unless you have an SRC).

[sonare]

I have a preview copy of an orchestral CD recorded at Abey Road with all digital Neumann and Sennheiser mics. You cannot imagine a cleaner sound! You cannot imagine a sound with less life!

I absolutely agree with Mark that this is a solution in search of a problem. If you only wanted to use a pair things might be a little different. Even if money were no object and technology presented no barriers (combining digital and analog mics) I would still stick with the old-fashioned stuff, It is about the sound, n'est pas?

Rich

[d_fu]

Originally Posted by BrianHanke

The signals from the two mics will inevitably be slightly desynchronized.

Correct... Plush repeated what I said already...

The problem comes when the master device (in my proposed case, one of the Konnekt 8s) polls both mics with reference to a single clock.

Umm... No. The Konnekt can not be master. Even in a (working) setup with only one digital mic and one Konnekt, the mic would have to be master (i.e. the Konnekt would have to sync to the incoming signal), because the connection kit is free-floating.
The problem is that two such independent setups won't work together because they are not in sync. There can only be one master, i.e. one device that runs on its own clock without syncing to others. But here, you'd have two (the mics).

There will be times when one mic is between samples and that's when a click will happen.

If you make one of the Konnekts master, both mics will cause clicks. So at least you'd get that in stereo...

However, with a sample rate converter, the gaps between samples will be interpolated so that data can still be recorded even if the original signal is between samples. Am I on the right track here?

SRC doesn't interpolate gaps... It will continuously resample the entire signal of all incoming signals to one specific sample rate, which could be the SRC device's internal Fs, or something you feed it by Word Clock. SRC in this case doesn't mean from e.g. 48 to 44, but from 96000.04 to 96000 (i.e. the master sample rate for all units).

Originally Posted by Plush

I think a digital mic experiment would be fun. I wonder if a difference could be heard?
(between a digital mic and the same mic plugged in to a neutral mic amp into a top a/d converter ? Methinks there would be no difference but I keep an open mind.

Only Schoeps and Sennheiser SDCs would allow such an experiment, they are the only ones that will allow identical capsules on analog and digital preamps.

Originally Posted by sonare

I have a preview copy of an orchestral CD recorded at Abey Road with all digital Neumann and Sennheiser mics. You cannot imagine a cleaner sound! You cannot imagine a sound with less life!

Would you think that is because the very nature of these mics? The old digital vs. analog question? I have that Neumann demo disk somewhere... Need to find it and listen to it...

[BrianHanke]

Hmmm... I'm lost now. I need to find some papers about the workings of SRC and read up on the science behind it all. I completely trust that using S/PDIF connection kits isn't going to result in a usable stereo recording, but I'm very curious to learn about the underlying technical reasons. Many thanks for your time and the assistance you've offered!

Originally Posted by d_fu

SRC doesn't interpolate gaps... It will continuously resample the entire signal of all incoming signals to one specific sample rate, which could be the SRC device's internal Fs, or something you feed it by Word Clock. SRC in this case doesn't mean from e.g. 48 to 44, but from 96000.04 to 96000 (i.e. the master sample rate for all units).

[Roland]

I still go back to the point that if you are recording a signal registering at 80db SPL and the mic is say rated at 141 db SPL, on a thats recording your signal at 14 bit resolution. Now if anyone can tell me why that is a good idea I'd like to know. And as for the "quasi" 27 bit conversion, I don't buy into the psuedo science either. If we were seriously losing that much quality in the cable I could be convinced, but I'd take a bet none of us in here could tell the difference between 1 foot of mic cable and 100. Coupled with the factor you are now dealing with the manufacturers own AD and mic pre, which has the limitation on it's size as it has to fit the mic body. I'm with those that think it's a solution looking for a problem.

Regards


Roland

[d_fu]

Originally Posted by BrianHanke

Hmmm... I'm lost now. I need to find some papers about the workings of SRC and read up on the science behind it all.

Start here: Sample rate conversion - Wikipedia, the free encyclopedia

I completely trust that using S/PDIF connection kits isn't going to result in a usable stereo recording,

With SRC (e.g. in the Marian card), it will...

Originally Posted by Roland

I still go back to the point that if you are recording a signal registering at 80db SPL and the mic is say rated at 141 db SPL, on a thats recording your signal at 14 bit resolution.

Not sure I understand the math...

If we were seriously losing that much quality in the cable I could be convinced, but I'd take a bet none of us in here could tell the difference between 1 foot of mic cable and 100.

Part of the idea may be that the digital connection will be less prone to interference (cell phones), I guess.

Daniel

[BrianHanke]

Yes, I read that article already, and it’s where I got the information about SRC involving interpolation. It seems to me that dealing with two separate signals from digital mics would involve case (b), wherein the samples are treated as a time series and any needed new points are created by interpolation. However, it seems you said this isn't the case, which is why I want to read up in more detail.

Originally Posted by d_fu

Start here: Sample rate conversion - Wikipedia, the free encyclopedia

[Roland]

Originally Posted by d_fu

Not sure I understand the math...

Daniel

141db spl has to be within the maximum dynamic range of the mic, (24 bit), a signal 60db spl lower would be 10 bits lower in level. If this is your maximum level, quite possible in classical work you signal is only resolved to 14 bit equivelent, in a seperate mic/AD converter set-up you can easily get to within 22 bit resolution in the convertor.


Roland

[sonare]

Originally Posted by d_fu

I have that Neumann demo disk somewhere... Need to find it and listen to it...

I can assure you that you do not have this disc-- it was sent by a producer colleague and has not been released yet.

This is a real-world recording-- not a demo disc designed to showcase the product.

Rich

[d_fu]

Originally Posted by Roland

141db spl has to be within the maximum dynamic range of the mic, (24 bit), a signal 60db spl lower would be 10 bits lower in level. If this is your maximum level, quite possible in classical work you signal is only resolved to 14 bit equivelent, in a seperate mic/AD converter set-up you can easily get to within 22 bit resolution in the convertor.

Just for the record, Neumann specifies the TLM 103 D (LDC) at 134 dB, the SDCs are in that vicinity.
And then, the conversion doesn't just sit there working with the unamplified signal... And it's not just 24 bit. We've discussed gain staging at length earlier. Interfaces like Neumann's DMI-2, DMI-8, or the RME DMC-842 feature a gain setting for the digital microphones, so you don't lose resolution. Even the little interface box with my Beyer digital mics allows gain control from -20 to +36 dB.
Without the DMI or other interfaces, the Neumann mics have a preset gain of 10 dB. Loss of resolution is a non-argument, IMHO.

[boojum]

I think I'll wait until digital mics are "plug and play." It is a little early in the development cycle to suit me, and my pocketbook. My analog mics are working just fine.

[BrianHanke]

Agreed! They are SO close to making it plug and play. It would be a dream come true to be able to simply plug a digital mic (or mics) directly into a computer for recording. No more external preamps and converters means less stuff to worry about, less stuff to carry around, and less stuff to break.

It would be so trivially easy for any manufacturer to make an all-digital interface with multiple S/PDIF and/or AES/AES42 inputs. Admittedly Marian does offer something like this, but the fact that it's PCI limits its usefulness.

Originally Posted by boojum

I think I'll wait until digital mics are "plug and play." It is a little early in the development cycle to suit me, and my pocketbook. My analog mics are working just fine.

[mpdonahue]

Originally Posted by d_fu

Just for the record, Neumann specifies the TLM 103 D (LDC) at 134 dB, the SDCs are in that vicinity.
And then, the conversion doesn't just sit there working with the unamplified signal... And it's not just 24 bit. We've discussed gain staging at length earlier. Interfaces like Neumann's DMI-2, DMI-8, or the RME DMC-842 feature a gain setting for the digital microphones, so you don't lose resolution. Even the little interface box with my Beyer digital mics allows gain control from -20 to +36 dB.
Without the DMI or other interfaces, the Neumann mics have a preset gain of 10 dB. Loss of resolution is a non-argument, IMHO.

I've actually spent most of my career trying to avoid Cascaded/Gain ranging A to D converters. Normally, the crossover region between the 2 converters is right in the middle of the dynamic range where most classical music resides (-36 to -18 dBFS). We've owned the Prism and Lavry converters (Which both use this topology) and could never get by the weird non-linearity that happened in this region of the dynamic range. They are great converters for rock and roll, but for classical they have always fallen short for me.
As to the digital gain thing, most of the people who don't have any problems with digital gain probably didn't live through the 1630/DAE-3000 era. Basing a system on under modulating gain ranging converters and making it up with digital gain terrifies me. You can't get the precision back by adding gain after the conversion. Or maybe I just don't understand this new fangled digital theory.

As always YMMV.
All the best,
-mark

[Don S]

Yes, the little neumann converter box is expensive, but I have to say that the KM184D was a very impressive mic and probably worth it. The neumann rep told me they were having trouble moving these. I mentioned the expense of the box and the fact that upon a glance, only the single"D" separated these from the dreaded 184.

[BrianHanke]

Ah, I want one (or two)! Here's the thing: $2300 for the mics, $1000 for the DMI-2 and, I don't know, maybe $1500 for a Digital Konnekt X32 or something similar to hook it up to the computer. The DMI-8 looks more useful (it has ADAT out), but I'm sure it isn't remotely affordable. We're talking too much money for something that can only be used with a tiny number of AES42-compatible microphones.

Originally Posted by Don S

Yes, the little neumann converter box is expensive, but I have to say that the KM184D was a very impressive mic and probably worth it.

[John Willett]

OK - I am out of the country in Slovakia and only looking in occasionally.

Plush is correct - if you want to run a pair of KM-D with Neumann connection kits you *must* go through a sample-rate converter to clock them.

Otherwise use the DMI-2 (or DMI-8 or RME 842 or SD 788T).

You *can* use a pair of Sennheiser MKH 8000 series with a single MZD 8000 digital adaptor through a single Neumann connection kit (I have been doing exactly this on my Nagra VI).

I have a pair of KM-D with 183 and 131 heads, DMI-2 and Sennheiser MKH 8000 series with MZD 800 so am well conversed with using digital mics in anger.

(PS - I am happy to answer any PMs on digital mics if that will be easier).

[BrianHanke]

Now this is interesting. Can you explain how this system works? How are the MKH mics attached to the MZD unit? Is there any chance of Neumann creating something like this for the KM series?

Originally Posted by John Willett

You *can* use a pair of Sennheiser MKH 8000 series with a single MZD 8000 digital adaptor through a single Neumann connection kit (I have been doing exactly this on my Nagra VI).

[d_fu]

Originally Posted by John Willett

Plush is correct - if you want to run a pair of KM-D with Neumann connection kits you *must* go through a sample-rate converter to clock them.

Just what I said, too...

You *can* use a pair of Sennheiser MKH 8000 series with a single MZD 8000 digital adaptor

How do you physically connect two capsules to one MZD 8000?


Anybody tried any Schoeps digital mics here?


Daniel

[Teddy Ray]

I fail to see the point. I tried some digital mics towards the end of my time in Germany, and while they were ok, the sound was certainly nothing to rejoice over.. the fact that converter technology is continually moving forward makes the digital mic thing even less attractive.

this is a bad trend, trading sound quality for convenience. (IPOD?)

[d_fu]

Originally Posted by Teddy Ray

I tried some digital mics towards the end of my time in Germany, and while they were ok, the sound was certainly nothing to rejoice over..

Care to specify which mics you tried and what you compared them with?

[John Willett]

Originally Posted by BrianHanke

Now this is interesting. Can you explain how this system works? How are the MKH mics attached to the MZD unit? Is there any chance of Neumann creating something like this for the KM series?

The MZD 8000 is inherently stereo - Sennheiser plan to do a Y-cable to go with the system and I am trialling a pre-production unit which will shortly be going for review.

[John Willett]

Originally Posted by d_fu

Just what I said, too...

Sorry, I was in an airport departure lounge and only skimmed the thread.

Originally Posted by d_fu

How do you physically connect two capsules to one MZD 8000?

WIth a Y-cable - I have a pre-production sample (see above).

Originally Posted by d_fu

Anybody tried any Schoeps digital mics here?

No - the Schoeps are mode-1 only and *have* to go through a sample-rate converter. But I would expect the digital version to be up to Schoeps normal high quality

[John Willett]

Originally Posted by Teddy Ray

I fail to see the point. I tried some digital mics towards the end of my time in Germany, and while they were ok, the sound was certainly nothing to rejoice over.. the fact that converter technology is continually moving forward makes the digital mic thing even less attractive.

Which ones did you try? The early Beyer is nothing like the AES42 standard digital mics by Neumann, Schoeps and Sennheiser.

Originally Posted by Teddy Ray

this is a bad trend, trading sound quality for convenience. (IPOD?)

This is rubbish as there are a *lot* of advantages to digital mics if you just stop and think about it - which is why a French PA company have now gone totally digital from the mics.

[BrianHanke]

Thank you John ~ informative as always! Do you have any insight you can share regarding Neumann's plans for its digital lineup? A Y-cable adapter similar to the one you described would be most welcome in the KM D series.