• Registered: 2009-06-30
  • Posts: 217

Topic: Gain structure Octamic XTC - 12Mic

I have one XTC and two 12Mics.

Why do you not make these units with the same sensitivity? XTC has 12dBU max input Mic level, 12Mic has 18 dBU. That means I have a discrepancy of 6dB, that I have to remember to add mentally to the XTCs gain. Or the other way round: I have to crank up the gain 6dB more on the 12Mics.
OK, it is not that hard to do, nevertheless I would expect them to be the similar.

Is there a chance to fix this with a firmware update on the XTC? (The 12Mic behaves more like I am used to, the XTC is indeed very sensitive.)

Anyone else?
Georg

2 Reply by ramses (edited by ramses 2022-02-12 16:17:37)

  • ramses
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  • Registered: 2012-10-14
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Re: Gain structure Octamic XTC - 12Mic

Hi Georg, how are you ?

12Mic has been released 7y later as the XTC (~2013 vs 2020) and thus uses other / more modern converters with different technical specs.

XTC: Gain range of 65 dB // accepts signals of up to +12 dBu (with PAD for 4 of the 8 inputs up to +32 dBu)
12Mic: PAD-free microphone input stages with 75 dB gain range // accepts signals of up to +18 dBu

XTC   : gain range 65dB, control range 55 dB (0, 10-65 dB).
12Mic: gain range 75dB, control range 75 dB (in 1dB steps over the whole range).

With this comparison of technical data I want to show, that it's not possible to use the same gain settings / "numbers on a knob or fader" when (gain and) control ranges are so different like in this case: 55dB for XTC, 75dB for 12Mic.

It's better for the product, if RME makes full use of 12Mic's new converter's capabilities and designes the circuits to allow for higher gain ranges or to be able to get rid of PAD. All with the goal to achieve best technical results in terms of e.g. SNR/dynamic, gain range,  input level stability and what not.

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14

3 Reply by georgob (edited by georgob 2022-02-13 13:52:25)

  • Registered: 2009-06-30
  • Posts: 217

Re: Gain structure Octamic XTC - 12Mic

I understand all that. But I do not care about the internal analog structure - the important thing that matters in a digital Mic Preamp is: How does my mic level of e.g. -54dBU translate into the digital world in dBFs? How the internal AD conversion is done, at what dBU 0dBFs is reached, is not important to me during recording. Then I only care about the "Gain". I am not that nerdy to want a "sensitivity" instead of gain (as I recall from the directout andiamo), but just that the gain numbers match between RME devices.

It would be a matter of offsetting the XTCs Gain numbers by 6dB. Its just a numbers thing. It can still have its Gain range of 65 dB, but the control range would be (6, 16-71dB).

Then it would perfectly match the 12mic and I think it could be done with a simple firmware update.

Georg

4 Reply by ramses (edited by ramses 2022-02-13 15:23:44)

  • ramses
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Re: Gain structure Octamic XTC - 12Mic

Hi Georg, I thought I had found a plausible explanation for this, but of course I could be wrong.
If I have not misunderstood you in your last post, then you are trying to establish relationships between dBFS and dBu, which actually do not exist, see also Sengpiel http://www.sengpielaudio.com/calculator-db-volt.htm.

Maybe RME can bring more clarity here .. Otherwise, have a nice rest of Sunday.

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14
  • Registered: 2009-06-30
  • Posts: 217

Re: Gain structure Octamic XTC - 12Mic

I just want to amplify the same microphone the same amount on both 12mic and XTC and get the same digital level.
I like to know what I am doing and this would simplify the recording setup and put my mind at ease - at the same time standardize my setup for other people who use it.
It is similar with the Micstasy (I do not own), It has 21dBU max input level @0dBGain. Compared to 18dBU (12Mic) and 12dBU (XTC). In order to get the same digital level I have to gain 9dB more one the micstasy and 6dB more on the 12Mic to get the same digital level as the XTC. Go figure. And this discrepancy in one brand.
Again: I think I understand why this has to be, and also the analog component of it all. But lastly it just comes down to some Gain numbers that sit between the analog and digital world.
Georg

Georg

  • Registered: 2021-09-15
  • Posts: 14

Re: Gain structure Octamic XTC - 12Mic

Georg, I totally understand your view, but I also understand that this has technically rather low priority. The wish for comparable outputs actually would result in wishing for microphones that all have the same sensitivity.
Besides being a musician and recording artist I do some programming also. Aiming for the same thing as you, I am working on a recording app that is capable of normalising audio based on mic sensitivity, mic gain and - later - also the AD specs. To avoid quality loss the resulting audio needs to be 32bit float.

It should be possible to calculate the incoming dBu into dBFS. Therefore you need to measure, at which dBU the AD converter outputs 0dBFS. Currently I am assuming this is the value for max. dBu input given in the specs. I am not 100% sure if this is correct. I also made a little calculator that deals with the gain structure and noises: http://www.stefan-kiessling.de/noisecalculations

  • Registered: 2012-01-10
  • Posts: 8

Re: Gain structure Octamic XTC - 12Mic

I'd absolutely endorse Georg's request for comparable gain values (or numbers) across the different preamps.
One of my clients has a setup with a mix of XTC and Micstasys, and from a user's perspective it simply doesn't make sense to be forced to calculate gain values every time. Especially in classical recordings with a significant number of similar or identical microphones (e.g. same type of mic for all strings or for all perc) this situation occurs regularly. Always thinking about which preamp a mic is plugged into is absolutely not what you want for a smooth workflow. Reading that the reference is different once more on a 12Mic makes it even worse imho.