1 Topic by mike G (edited by mike G 2022-12-26 10:10:23)

  • Registered: 2022-12-18
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Topic: Bypass RME Pre Amps - back anolog inputs?

I'm a little confused with page 40 of the manual regarding reference levels.

"So to get +4 dbu, you use 13dbu in Total mix on the channel and ADD 9dbu of gain with the gain rotary"

I have two questions here:

  • I'm using my own pre amp, if 13dbu is the default in the channel, it seems like the Fireface UCX II is using some pre amping. How can I bypass this so I'm just using my own pre amp going straight through?

  • And I'm not even sure I'm understanding page 40. +4 dbu would be 0dbV on an analog system, and would equate to -18 on a digital system level meter. So if I am adding 9 dbu of gain, would that bring the -18 digital level up to 0 dbfs on a digital system?

I think I understand the concept of line level, but I'm not sure I understand how total mix is powering the line levels in the background.

2 Reply by ramses (edited by ramses 2022-12-26 12:43:06)

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Re: Bypass RME Pre Amps - back anolog inputs?

As the manual states in ch 19, 20 and 39 (technical specs, which is btw an excellent summary of technical data, also regarding the number of supported reference levels, digital gain, etc).

The analog
- inputs support two different reference levels / "input sensitivities": switchable to +19 dBu and +13 dBu
- output support three different reference levels / "output level" switchable to +19 dBu, +13 dBu, +4 dBu

Typical reference levels are +24, +19, +13, +4 dBu and consumer level -10 dBV.

If you connect external devices to your analog inputs, then you need to choose a reference level / sensitivity so that the signal is for the A/D converter in an optimum range to perform the conversion.
If the input signal is
- too loud / the sensitivity too high, then you get distortion.
- too silent / the sensitivity too low then the AD converter gets a signal which is too low, the result is less dynamic and a lower SNR.

If you want to make your inputs more sensitive for lower signals, you can adjust this by using digital gain, which is adjustable from 0 to 12 dB. You find reference level settings and the digital gain knob in TM FX by clicking the "wrench/tool" symbol at the input fader.

Example: +4 dBu
If you would like to reach the typical studio level of +4 dBu then set the sensitivity of the inputs to +13 dBu, then add +9 dB of digital gain, and you have +4 dBu studio level (13-9=4).

Example: consumer level -10 dBV
If you would like to reach consumer level, then you would need 20.8 dB of digital gain to bring the input sensitivity from +13 dBu to consumer level (-10 dBV = -7,78 dBu). Select +13 dBu and add the maximum gain of 12 dB. The 20,8-12= 8.8 dB less sensitivity are tolerable. Let's say you have more threshold for peaks by this.

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

3 Reply by mike G (edited by mike G 2022-12-26 21:59:56)

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Re: Bypass RME Pre Amps - back anolog inputs?

But you didn't mention. When you're adjusting sensitivity, it seems like you're using some kind of pre amp built into the Fireface. To my original question: is this a resistance ohms circuit adjusting the sensitivity, or more specifically a pre amp sending more gain down the line?
I wanted to know how to bypass any pre amp and use my own external Mic pre on the back in puts. Or are these just sensitivity circuit's where there is no pre amp happening?

Sorry ramses
I'm sure it's an  excellent summary, but only if you understand levels. I've been reading sites about db dbu..ect for a few weeks and the examples always end up getting to deep into the math and then I'm lost. Also, understanding this stuff is not always just about the concept, but all the different references confuses people because most people learn by comparing something to something solid. I know not everything worked this way in life, which makes this subject difficult. You're taking consumer, but I'm not using consumer gear, so I would say for simplicity, keep one example line level for all other examples.

I don't understand why the outputs support switchable reference levels of +4 but the inputs doesn't in your example. Makes no sense to me. But then you go on to a bunch of other things. I'm guessing I need to set my +4 gear to 13db (which is the default) not sure why you said dbu then db, that is another source of confusion I'm still working out. ATM, I'm just starting out trying to keep my levels under at around -6 db . I realize there is a sensitivity, or a so called sweet spot in levels for the converters, but page 40 image of the four reference levels makes no sense to me at this point because they're vague example's to someone inexperienced in levels.

This example makes no sense to me, I'm sure it does to you, just not me.
The 2nd column 0dBFS @ and the 4th column 0dBFS@ say the same thing except the data underneath it say different levels.
I'm not sure how to make sense of this chart. That was really the source of my confusion.
www.pyramid-of-wisdom.com/ref.jpg

I'm off reading. Hopefully this will all make sense one of these days.

4 Reply by ramses (edited by ramses 2022-12-26 22:00:16)

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Re: Bypass RME Pre Amps - back anolog inputs?

Mike, I wrote everything that you need to know.
Now it is your turn to simply accept, that analog inputs can / must have different levels of sensitivity,
because the devices that we connect to it have different output levels.

You cannot connect a +19 dBu output signal to an analog input whose sensitivity has been increased to manage low level consumer input, this should be clear.

All that you need to do is to simply make an experiment.
Connect, e.g., a player to an analog input and observe simply the input level when you switch between different reference levels. You will notice that the higher the reference level is, the lower the RMS/peak signal will be because when selecting higher reference levels the input is more insensitive to be able to accept hotter signals.

I would simply play with the equipment and make these little observations that are easy to perform.

Then maybe read my text repeatedly and then the penny will drop.

I hope / think the basic concept of not overloading an input is clear to you and that its also not wanted to record a signal which is too weak.

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

5 Reply by mike G (edited by mike G 2022-12-27 06:30:25)

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Re: Bypass RME Pre Amps - back anolog inputs?

I do understand the first concept. I've always known you have to match the input to the outputs. It's like you wouldn't drive an amp on a phone playing through your car stereo to 90% and keep your car stereo vol at 10% And then there's are impedance levels.

But I edited my post, you might have missed it.
I don't understand that chart.

6 Reply by mike G (edited by mike G 2022-12-26 22:20:16)

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Re: Bypass RME Pre Amps - back anolog inputs?

I see what you mean, when you said

"You will notice that the higher the reference level is, the lower the RMS/peak signal will be because when selecting higher reference levels the input is more insensitive to be able to accept hotter signals."

That changed my way of seeing this.  So the higher the number, the hotter the signal it expects. Makes sense how this works now. Do you see where I got confused? I thought the higher number meant you were adding more gain from some kind of amp in the fireface. But this is a reference, which make sense. I didn't see it that way at first.

So if I set my reference to say 13dbu, I don't need to use the gain control in Total Mix, I should be able to just add more gain with my gain knob on my mic pre. Is there a way to totally bypass the pre amp in the Fireface? I don't' know if leaving the gain knob in total mix is really bypassing. Maybe it is though.

7 Reply by ramses (edited by ramses 2022-12-29 09:11:49)

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Re: Bypass RME Pre Amps - back anolog inputs?

> Is there a way to totally bypass the pre amp in the Fireface?

I assume you mean the analog inputs, not the mic inputs of the UCX II, as we talked a lot about analog line inputs.

Analog inputs work on "line level", they have no "pre-amp" as we know it for microphones.

You might be irritated that the analog inputs support different line levels and have a digital gain knob.
It might look to you like a preamp, but in fact it isn't.

The task of a preamp is, to bring very low signals - like of a microphone - to line level. You need high amplification for that. Therefore, preamps have typically a gain of more than 55 dB, the UCX II integrated mic preamps even support up to 75 dB amplification (also called gain).

The different reference levels need to be there to better connect analog devices to each other on "line level" so that the levels better match to each other (as for line level different standards for "signal levels" exist: different studio levels and consumer level).

The digital gain resides in the digital domain to increase the volume a bit further if required. Otherwise, RME would need more circuits (electronic) on the board for supporting more line levels. I can only assume that this increases cost and makes the circuit more complex, therefore only two analog reference levels and a digital gain of up to 12 dB.

> I don't' know if leaving the gain knob in total mix is really bypassing

If you do not want - or better said - "need" the digital gain, then simply keep it at zero.

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14
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Re: Bypass RME Pre Amps - back anolog inputs?

If there is even a way to do it, you dont have to "turn off" preamps. If you have an external pre, just apply the nescessary gain/sensitivity to match like Ramses describe.
This topic has been discusssed and to my knowing there is no such switch.

ADI-2 DAC, ADI-2 PRO, DigifaceUSB, UCXII, ARC, HEGEL.h80, KEF.ls50, HD650, ie400pro _,.\''/.,_

9 Reply by mike G (edited by mike G 2022-12-29 05:27:52)

  • Registered: 2022-12-18
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Re: Bypass RME Pre Amps - back anolog inputs?

Thanks guys
@ramses. Wanted to follow up with you.

Yes,thumbs up to the analog digital gain. I was not aware of all this. That was a new term I learned about today. You might have mentioned it last night. Good explanation on post #7 on all points. And you're right, RME choose a good compromise by using digital, which should be transparent.

I was talking to a RME tech from the US branch on the phone today who clarified something I was not understanding on that image chart below. I put what you said last night together with what he said:
What I wasn't understanding, but now do, was this: when you add db of gain, the reference mark comes down, not increases. I didn't get this concept last night, but I do now. Also, these numbers on the chart below are levels that focus on sensitivity. The problem was, I was thinking about them as levels on digital meter. But I get it now. So if I chose a reference of 13dbu in Total Mix, and I wanted to achieve a +4dbu signal, I would add 9db gain just as the manual and chart below says. 13 - 9 = +4 And I believe I read something that +4dbu line level on a digital meter such as in Logic Pro is around -18.
I believe I understand it better now.
----

By the way, I tested what you said about the level difference from 13dbu to 19dbu. And you are right. Changing it to 19 lowered the meter because the sensitivity in the Fireface changed to expect a hotter signal.




http://www.pyramid-of-wisdom.com/ref.jpg

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Re: Bypass RME Pre Amps - back anolog inputs?

Also interesting to read: https://www.elysia.com/de/18dbfs-is-the-new-0dbu/

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

11 Reply by mike G (edited by mike G 2022-12-31 21:19:28)

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Re: Bypass RME Pre Amps - back anolog inputs?

Thanks Ramses. Reading it now!

I also found this at work today. I knew about the .775 he talks about, but the story about the bell was interesting. And why they used 0 as the center point.

https://youtu.be/3n-ujzwiRdA

This guys pretty good too
https://www.youtube.com/watch?v=xSe7y9tYex8

12 Reply by mike G (edited by mike G 2022-12-31 21:38:09)

  • Registered: 2022-12-18
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Re: Bypass RME Pre Amps - back anolog inputs?

Ya, That link you posted ramses was good. For me, it clarified that dbu is for analog and dbfs is use for digital. And some other great points like the fader resolution being logarithmic and having more resolution at the upper/top fader.
Also, it's now clear to me how voltage works, that when you apply .775 volts, you get 0dbu in the analog world, but that same voltage amount would register as a -18dbfs in the digital world. Different units of measurement.

Also, here is another great example on the noise floor with audio samples by Marcus Hutsell. Some of this is common sense, but still a great example for new guys.
https://www.youtube.com/watch?v=6KbR-hb4HS8