1 (edited by mark2748 2020-11-30 00:12:26)

Topic: ADI-2 DAC FS output levels and S/N

Based on Ramses' outstanding post for the ADI-2 PRO FS

https://forum.rme-audio.de/viewtopic.ph … 24#p155724

I created a similar spreadsheet for the ADI-2 DAC FS (updated 11/29/2020 to v1.2):

https://www.dropbox.com/s/wu84nvyxqqwf7 … 2.pdf?dl=0

Signal-to-noise is calculated for Auto Ref Level = ON.

No guarantees, any comments/corrections welcome.

2 (edited by mark2748 2020-11-23 23:02:32)

Re: ADI-2 DAC FS output levels and S/N

So far I believe all my spreadsheet numbers are correct, in that they match up with examples in the User Guide and random forum posts.

However, I am not clear on how to calculate S/N in the 0.5 dBr to 6.0 dBr region (left blank).  Would the S/N just keep increasing in 0.5 dB steps from the respective 0 dBr specification value, remain fixed at the 0 dBr value, or decrease for some electronics reason? 

Same question applies when boosting the volume up from 0.0 dB to 6.0 dB from the three other reference levels, with Auto RL off.  What does the S/N do?

Fine points, all probably inaudible and academic, but I would just like to know for completeness.

3

Re: ADI-2 DAC FS output levels and S/N

With the latest AK4493 versions (DAC and Pro) SNR improves up to 2.5 dB, following the volume setting of 0 dB up to +2.5 dB (I thought I mentioned that somewhere in the manual). For higher volume settings as +2.5 dB, and the  AK4490's 0 dB to +6 dB volume there is no change in SNR, as the max level is already reached at +2.5 dB and 0 dB respectively.

Regards
Matthias Carstens
RME

4 (edited by mark2748 2020-11-24 18:11:48)

Re: ADI-2 DAC FS output levels and S/N

MC wrote:

With the latest AK4493 versions (DAC and Pro) SNR improves up to 2.5 dB, following the volume setting of 0 dB up to +2.5 dB (I thought I mentioned that somewhere in the manual). For higher volume settings as +2.5 dB, and the  AK4490's 0 dB to +6 dB volume there is no change in SNR, as the max level is already reached at +2.5 dB and 0 dB respectively.

Thank you very much for the clarification, which I have never seen explicitly documented anywhere else (though it is briefly mentioned in the new product description on RME's web site).

I updated the S/N (Auto RL) for the +13 dBu cases in the spreadsheet accordingly (now v1.1).

5 (edited by mark2748 2020-12-02 08:40:18)

Re: ADI-2 DAC FS output levels and S/N

Here is a spreadsheet which calculates output level and S/N for manual setting of the ADI-2 DAC FS volume (Auto Ref Level = OFF)  Updated 12/01/2020 v1.3:

https://www.dropbox.com/s/6nvxxetk9p1f7 … 3.pdf?dl=0

The spreadsheet confirms that the best S/N (largest dynamic range) is expected by choosing the hardware reference level (one of four) which provides output closest to the desired level, i.e. with volume control near 0 dB.

6 (edited by mark2748 2020-11-30 01:21:18)

Re: ADI-2 DAC FS output levels and S/N

I corrected the Auto RL and Manual Level spreadsheets linked above to correctly list the limited maximum output values for dBr = 3.0 to 6.0 and dBu = +13, dB = 3.0 to 6.0 respectively.  I think they now agree with User's Guide Sections 19.2 Line Out RCA and 19.3 Line Out XLR.

Re: ADI-2 DAC FS output levels and S/N

MC wrote:

With the latest AK4493 versions (DAC and Pro) SNR improves up to 2.5 dB, following the volume setting of 0 dB up to +2.5 dB (I thought I mentioned that somewhere in the manual). For higher volume settings as +2.5 dB, and the  AK4490's 0 dB to +6 dB volume there is no change in SNR, as the max level is already reached at +2.5 dB and 0 dB respectively.

I understand that for ref level = +13db the max possible output volume is achieved at +2.5 dB.

What happens for the other three reference levels? Does their output also get limited at +2.5 dB, or does it continue to increase up to +6.0 dB with corresponding improvement in S/N?

I did a crude test at -5 dBu and it seems volume keeps increasing up to +6.0 dB, though it is hard to know for sure since the Analyzer horizontal bars enter saturation beyond +2.5 dB for my source.  As a practical matter, should one run at +2.5 dB or less to preserve headroom anyway?

8

Re: ADI-2 DAC FS output levels and S/N

+2.5 dB is the digital limit for full scale signal (0 dBFS). You saw the level rise higher, but when analysing the waveform you will see distortion as well (clipping).

Regards
Matthias Carstens
RME

9 (edited by mark2748 2020-12-02 18:33:46)

Re: ADI-2 DAC FS output levels and S/N

MC wrote:

+2.5 dB is the digital limit for full scale signal (0 dBFS). You saw the level rise higher, but when analysing the waveform you will see distortion as well (clipping).

Thanks for the additional information.

Since it is unclear to me if there is a hard clamp on the output voltage at +3.0 dB and above (which might make the S/N constant), I "punted" and called the S/N unspecified in this volume region for each reference level. 

Also, I assumed all along that the 0 dBFS specifications apply at Volume = 0 dB.  If true, then at Volume up to +2.5 dB there would be a S/N boost of up to +2.5 dB.  Is this correct, or do the 0 dBFS specs apply at Volume = +2.5 dB?

I try to capture these interpretations in the updated Output Level and S/N spreadsheet for manual volume adjustment (Post 5 above, v1.3).