1 Topic by user317 (edited by user317 2024-08-17 20:29:35)

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Topic: [adi-2 dac fs] dBr and resulting voltages using auto ref level

I have a question of understanding regarding resulting output voltage levels using auto ref level on an adi-2 dac fs using the XLR output.

   0 dBr    ->   +19 dBu    ->    6.9   Vrms
  -6 dBr    ->   +13 dBu    ->    3.47 Vrms
-12 dBr    ->     +7 dBu    ->    1.73 Vrms
-18 dBr    ->     +1 dBu    ->    0.87 Vrms

Did I understand it correctly?

If the sensitivity of the power amp is given with 1.6 Vrms, the voltage would be reached with ~ -12.5 dBr.

My power amp, a T+A A200, based on Purifi's Eigentakt modules, provides a very fast safety circuit which signals clipping among other sings or even switches off if there is an overload.

As I'm mostly listening to classical music, which usually is recorded rather quiet fortunately, I'm anyway reaching -5 dBr without any signs of distortion (optically and acoustically). Take this as an example starting at 41:09.

The final question therefore: Are my calculations correct?

Thanks for any correction or confirmation!

2 Reply by ramses (edited by ramses 2024-08-17 22:36:45)

  • ramses
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Re: [adi-2 dac fs] dBr and resulting voltages using auto ref level

Does my Excel help?

See https://forum.rme-audio.de/viewtopic.ph … 06#p165706

This file: https://www.tonstudio-forum.de/attachme … v003-xlsx/
(EDIT: update to v003, cosmetics, wrong background color, replaced purple with yellow marking)

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14
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Re: [adi-2 dac fs] dBr and resulting voltages using auto ref level

Yes, this file answers my question! I had not found this file yet! Thanks for confirmation.

That means using the auto ref level is the best for me to drive the T+A A200 amp w/o using any fixed levels, because I wouldn't be able to reach the full output of the device based on real world material, which isn't recorded @ 0 dBfs.

Thanks @ramses for your kind answer!

4 Reply by KaiS (edited by KaiS 2024-08-17 22:31:05)

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Re: [adi-2 dac fs] dBr and resulting voltages using auto ref level

Your calculations are correct.

I‘ve even seen the T+A spec‘s which show 1.6 V / 6.3 dBu sensitivity for full scale 250 W output.

This indeed equals -12 dBr on ADI-2 DAC‘s XLR, but only for a music track running full scale.

The linked Youtube music track, played on iPhone to ADI-2, shows almost full scale in the final movement.

With your setting of  -5 dBr you would overdrive the T&A amp by 7 dB, would be incredibly loud and heavily, audibly distorted.


As this likely isn‘t the case, you probably have significantly reduced the digital level somewhere in your chain.

Look at ADI-2’s Peak Meters, set to “Pre FX”:
• SETUP / Options / Display / Hor. Meter: Pre FX

You won’t see anything close to full scale, right?

You can even set the meters to “Post-FX dBu”, then you can directly read the dBu figures while playing the track.
You have to add 6 dB to the readings, as ADI-2 DAC references to the RCA out, which is 6 dB quieter than the XLR.

What do you see (with 6 dB added)?

KaiS's Website

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Re: [adi-2 dac fs] dBr and resulting voltages using auto ref level

user317 wrote:

Yes, this file answers my question! I had not found this file yet! Thanks for confirmation.

That means using the auto ref level is the best for me to drive the T+A A200 amp w/o using any fixed levels, because I wouldn't be able to reach the full output of the device based on real world material, which isn't recorded @ 0 dBfs.

Thanks @ramses for your kind answer!

You're welcome.
It was already available, but only as a screenshot.
After some additions (ADI-2/4 Pro SE) I added the complete Excel file.
BTW: v003 has only a small fix regarding background color, no changes in terms of numbers/calculations.

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14
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Re: [adi-2 dac fs] dBr and resulting voltages using auto ref level

Hi Ramses,

can you add TRS 3/4 balanced out with the corresponding ref levels to your list for the Adi 2/4 Pro?

That would be great.

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Re: [adi-2 dac fs] dBr and resulting voltages using auto ref level

Thanks Kai for your kind reply!

KaiS wrote:

With your setting of  -5 dBr you would overdrive the T&A amp by 7 dB, would be incredibly loud and heavily, audibly distorted.

As this likely isn‘t the case, you probably have significantly reduced the digital level somewhere in your chain.

That's exactly the point I'm stuck on and why I'm asking if I understood everything correctly.

The speakers are nubert nuvero 14. See page 6 for specs - sensitivity: 83.0 dB/1 W/1m (Basschalter voluminös), Nennbelastbarkeit 440 W. Therefore, they shouldn't be the bottleneck.

Bit perfect is true here - therefore, no manipulations on the feeding side: via USB / 48 kHz / flac (derived from the original opus track).

Switching to Pre FX gives me one peak level at -0.3 dBfs for the final chord. This would match what can be seen in audacity.

Looking at the RMS levels with

sox camille-saint-saens-last-chord.wav -n trim 0 0.01 stats : newfile : restart 2>&1 | grep 'RMS lev dB' | awk '{ print $4 }'|less

gives two times -9.8 dBfs - all other values are around -11 or -12 dBfs or less. Would that finally explain why no distortion can be heard and the protective circuit of the power amp doesn't detect anything and no LED shows any clipping?

Another possible thing would be, that the XLR cable to the power amp would attenuate the signal level. It's a microphone cable like this one.

Thanks for any hints!

8 Reply by KaiS (edited by KaiS 2024-08-18 12:12:11)

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Re: [adi-2 dac fs] dBr and resulting voltages using auto ref level

First: you’re really listening loud, do you?
My calculations say you’re at ca. 110 dBSPL with the Nuberts driven by full 250 W / channel.


If RME‘s meter “Pre FX” shows -0.3 dB at the final chord, that corresponds with what I get on that track.
So no attenuation in the digital chain.


Look at ADI-2’s Peak Meters, set to “ Post-FX dBu”:

• SETUP / Options / Display / Hor. Meter: “Post-FX dBu”
Now you can directly read the dBu figures while playing the track.

(You have to add 6 dB to the readings for the XLR dBu value, as ADI-2 DAC references to the RCA out, which is 6 dB quieter than the XLR.)

The amps clipping limit is reached at a actual shown figure “-12 dBu”.
There might be some 1 to 2 dB headroom in the amp for short peaks, so even -10 dBu meter reading might still be clean.
Everything above is definitely clipped / distorted.

Maybe the distortions are soft enough to stay inaudible.


And no, a standard mic cable of domestic length doesn’t attenuate the audio signal the slightest (OK, 0.001 dB smile with typical domestic impedances).

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9 Reply by user317 (edited by user317 2024-08-18 13:14:55)

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Re: [adi-2 dac fs] dBr and resulting voltages using auto ref level

The -0.3 dBfs are just milliseconds.

Please take a look at this screenshot:  https://i.ibb.co/QrgbGG9/image.png.

Most of the time, the dbFs is < -11 or -12 dbFs (as calculated by sox). I don't think -12 dBfs do result in 110 dBSPL. And yes, sometimes I like to hear the music a bit more loud - for a few seconds (the normal level for classical music is around -45 - -35 dBr)! It just feels great and it sounds perfectly clean and transparent. I can't hear any distortion even at -5 dBr. Is there a payable audio spectrum analyzer to check the output of the power amp? I'm really interested to see the actual values.

The post-Fx dBu level shows peaks around ~ +13 dBu (~ 3.5 V already including the +6 dB for XLR). I think that's what you are expecting.

Another interesting thing I just detected: for the dBu test, I removed the power cord from the amp (the amp was switched off at this moment). When starting the test, the amp LEDs went on (auto start if signal comes in) and it tried to start up - two times (each about 5 seconds - I already doubted that I removed the correct power cord)! Without any mains! This means: there must be huge elcos!

Addition:
the RMS of -11 / -12 dBfs actually covers the calculated max. -12 dBr. This means, the amp is driven at its limit at this moment. Correctly? I think that's the reason why I don't hear any distortion.

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Re: [adi-2 dac fs] dBr and resulting voltages using auto ref level

Minor short term clipping distortions stay unnoticed most of the time, if the amp behaves and doesn‘t go crazy.

Peak to long term average RMS ratio of music tracks typically is in the range of 10-20 dB.
The peaks are responsible for the clipping, the RMS for the perceived loudness.

In this track the ratio seems to be ca. 12 dB, so your listening loudness is about 98 dBSPL, with peaks at 110 dB SPL.
Guess you don‘t have neighbors, lucky you smile

Have a look here for the ear-healthy max. exposure times:
https://www.fldata.com/osha-noise-exposure-limits

https://www.fldata.com/wp-content/uploads/2022/07/OSHAs-noise-exposure-levels-Frontline.png

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Re: [adi-2 dac fs] dBr and resulting voltages using auto ref level

Thank you very much Kai for your care and your explanations. They help me a lot to classify correctly what I have observed.

KaiS wrote:

Guess you don‘t have neighbors, lucky you smile

That's mostly true. Anyway I use those high loudness levels only for a few seconds and rather rare - I don't want to go deaf :-). But sometimes I can't resist. It sounds (and feels!) so incredibly good!

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Re: [adi-2 dac fs] dBr and resulting voltages using auto ref level

whitenoiz83 wrote:

Hi Ramses,

can you add TRS 3/4 balanced out with the corresponding ref levels to your list for the Adi 2/4 Pro?

That would be great.

Yes, this and also for the ADI-2 Pro FS R BE, here (Excel v4):

https://forum.rme-audio.de/viewtopic.ph … 06#p165706

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14
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Re: [adi-2 dac fs] dBr and resulting voltages using auto ref level

Hi Ramses,

thanks for the quick addition to the list.

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Re: [adi-2 dac fs] dBr and resulting voltages using auto ref level

whitenoiz83 wrote:

Hi Ramses,

thanks for the quick addition to the list.

You're welcome.

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