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Measuring RME ADI-2 Pro with QuantAsylum QA401

March Audio

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#21

Miska

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#22
Presumably straight loopback?
What loopback? There's no loopback, computer playing test signal to the ADI-2 Pro AE and plot saved from audio analyzer. Balanced connection to the analyzer. IIRC, ADI-2 reference level set to +13 dBu.
 

SIY

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#23
Ah, sorry, I actually meant HpW-Works, I always confuse the two. I would use REW, it's getting better and better with each release. Its name, Room Eq Wizard, doesn't do justice to the vast functionality it offers today, it is a full measurement suite with better features than some $$$ software

I'm a fan of Virtins Multi-Instrument. Not easy to learn, but amazingly versatile.
 

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#24
Hi Matt,

Thanks a lot for the detail explanation! Really appreciate it!

When I have time I will re-test with the suggested values.
Hi Earfonia, Here's a walk through of a DAC evaluation with some new plug-ins. https://quantasylum.com/blogs/news/rapid-dac-evaluation

The plugins won't solve the problems you face trying to measure a $2000 DAC with a $450 QA401, but they might make it easier to see where you run into trouble in terms of margin. In the blog post, its a $99 DAC and the QA401 has lots of margin to measure that.

As you start your evaluation, if you run into any questions or curious plots, please just post for help
 

QAMatt

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#25
Hi Matt, thanks for your input. I did own a 401 however moved it on due to the rising noise floor (with increasing signal level) issue. Thing is (apart from your valid points regarding calibration) I can use a "professional" audio interface, achieve similar results but without the rising noise floor. What do you think the issue is here with the 401 and can it be fixed?
Hi March, I've attached a plot of the noise + distortion of the QA401 in loopback, but taken only up to -1 dBFS. In the plots I shared with Earfonia, those are 5 dB steps, and the last step is at +6 dBV = 0 dBFS, and the output is severely degraded.

But in the plot attached (which goes to -1 dBFS) you can see the QA401 loopback is very similar to the AK5397 graph (taken from the AK5397 spec).

Now, if you look at -15 dBFS, you can see the QA401 is a bit higher than the AK5397 graph, but remember you are looking at two devices here (the QA401 DAC which is a AK4490 and the QA401 ADC which is a AK5397) and they are both set to the same full scale of +6 dBV. So, the AK plot you are seeing the knee of a single device, but in the QA401 plot you are seeing the knee of both devices. So it's a bit higher

And yes, you could argue at around - 10 dBFS the QA401 N+d has crept up a dB or two versus the AKM plot, but I don't think it's unreasonable.

Yes, really good audio interfaces have been used for a very long time as the foundation of audio test setups, and many have designed interface boxes to cope with shortcomings. Fixed calibration and built-in SW controlled attenuator in a $450 box is pretty compelling for most consumer products that are being built today. I don't know of a product with those offerings that beats that price but maybe its out there.
 

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March Audio

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#26
Thanks Matt

I think the thd + noise plot sort of masks the issue.

Try plots of something like 1kHz at - 60dB, - 20dB and 0dB. Maybe 32 or 64 k fft. Observe the rise in the noise floor. My tests showed it to be significant.

Don't get me wrong, value for money is great, but this issue was a deal breaker for me I'm afraid.

It depends on usage, it could be fine for others requirements
 
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March Audio

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#28
What loopback? There's no loopback, computer playing test signal to the ADI-2 Pro AE and plot saved from audio analyzer. Balanced connection to the analyzer. IIRC, ADI-2 reference level set to +13 dBu.
It was a very simple question as to the measurement set up. There was no info about in your post.

i. e. was it the ADI generating signal then looped back into its A to D for measurement.

So, now we know that wasn't the case, what was the audio analyser being used?
 
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Miska

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#29
i. e. was it the ADI generating signal then looped back into its A to D for measurement.
No, it wouldn't look like that. Because ADI-2's ADC modulator noise slope begins to rise up from 60 kHz onwards (quite typical ADC chip, the noise floor with PCM looks just like DSD128 converted to PCM).

So, now we know that wasn't the case, what was the audio analyser being used?
OK, I thought it is apparent from the plot because it has the analyzer's logo. It is my Prism dScope III...
 

Miska

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#30
By the way, from the plot you can see the image leakage from the on-chip digital filter around 44.1k and 88.2k.

Running the DAC at 768k PCM or DSD256 with better external filters (and modulator) of course gets rid of those.
 

March Audio

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#32
No, it wouldn't look like that. Because ADI-2's ADC modulator noise slope begins to rise up from 60 kHz onwards (quite typical ADC chip, the noise floor with PCM looks just like DSD128 converted to PCM).



OK, I thought it is apparent from the plot because it has the analyzer's logo. It is my Prism dScope III...
Not interested in the out of band stuff and no it wasn't obvious.

What does the ADI loopback look like for the in band as it appears on paper that the ADI will out perform the Prism.
 
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March Audio

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#33
By the way, from the plot you can see the image leakage from the on-chip digital filter around 44.1k and 88.2k.

Running the DAC at 768k PCM or DSD256 with better external filters (and modulator) of course gets rid of those.
Why are you concerned about spuria at 105dB down at 44 + kHz?

Even with a poor amplifier any IM would be well below noise floor and in itself those signals are completely inaudible even if you speaker could reproduce them.
 
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March Audio

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#34
I think adi2 pro itself is a better analyzer than qa401. Why not just loop test?
It is but there issue of a considerable price difference.
 

Miska

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#35
What does the ADI loopback look like for the in band as it appears on paper that the ADI will out perform the Prism.
You can find those plots in ADI-2 manual, you can download the manual from RME website. For me it is not useful for measurements because the noise floor begins to tilt up too early. 20 kHz is not enough to inspect digital filter and SD-modulator performance.

It is very nice music ADC/DAC for recording and playing back music, that's why I have two ADI-2's. But it doesn't have performance or features of measurement systems. It doesn't outperform the Prism in practice, Prism is very conservative in their specifications.

For example ADI-2 doesn't have following things Prism has:
1) Accurate calibrated frequency and voltage measurements
2) Selectable input impedance, 150/600/100k
3) Wide input gain range, from microvolts to 159V
4) Flat noise floor

Why are you concerned about spuria at 105dB down at 40 + kHz?
Because it demonstrates non-perfect reconstruction of the signal and because I work specifically on digital filters and SD-modulators. That's why I cover measurements from 20 kHz bandwidth to 200 MHz bandwidth.

And I have absolutely no reason to tolerate such, or the images around 352.8 kHz that are just -50 dB down. Instead I can run it in a way that there are no images whatsover in the output, lower distortion in the audio band, at zero extra cost. So why would I accept worse performance when I can get better?
 

March Audio

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#36
Aahh so it's inadequate to look at the inaudible stuff ;) as I said I'm not interested in the inaudible.

Agree with the overall advantages of the Prism as a measurement system over the ADI but it is still interesting to see how they compare.

Non perfect doesn't matter if you can't hear it.

Isn't being good for music recording and playback somewhat the point?

Can you show this in band distortion created by the 352 kHz image? With real music level signals and not contrived test tones?

Why are you not concerned about say harmonic distortion in the audible band at - 120dB?

Actually let's not disrupt this thread. Please don't respond. I think you should start a thread where this can be specifically discussed.
 
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SIY

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#37
Aahh so it's inadequate to look at the inaudible stuff ;) as I said I'm not interested in the inaudible.

Agree with the overall advantages of the Prism as a measurement system over the ADI but it is still interesting to see how they compare.

Non perfect doesn't matter if you can't hear it.

Why are you not concerned about say harmonic distortion in the audible band at - 120dB?
All of the measurement issues with the ADI (or other good ADC/DACs) can be dealt with using a front-end signal conditioner like Pete Millett's soundcard interface or Jan Didden's Autoranger. The combo of the Autoranger with the ADI would be tough to beat at any kind of comparable price.
 

March Audio

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#38
All of the measurement issues with the ADI (or other good ADC/DACs) can be dealt with using a front-end signal conditioner like Pete Millett's soundcard interface or Jan Didden's Autoranger. The combo of the Autoranger with the ADI would be tough to beat at any kind of comparable price.
Thanks SIY, this is the reason I am very interested in the ADI. The advantages of the very expensive dedicated measurement systems start to greatly deminish when you make a combo as you suggest.

Ok, from the ADI manual

Screenshot_20190308-232736.jpg
 
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SIY

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#39
Thanks SIY, this is the reason I am very interested in the ADI. The advantages of the very expensive dedicated measurement systems start to greatly deminish when you make a combo as you suggest.
During Jan's last visit, we used the APx525 to measure the Autoranger- and the measurement limitation was the AP. What dedicated measurement systems like the AP or dScope get you is measurement efficiency and versatility, not necessarily better performance.
 

Miska

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#40
Why are you not concerned about say harmonic distortion in the audible band at - 120dB?
Of course I am also concerned about that, THD and IMD also gets somewhat lower. These things are naturally related!

Difference is smaller though than with ESS chips.


For me, the interesting parts of ADI-2 is the AKM chip's DSD Direct mode for playback, with access to all AKM chip's other features like digital filter selection, and especially DSD256 recording at very reasonable price. I've already had measurement systems for long time before ADI-2 appeared on the market, so I don't need it for measurement purposes.

P.S. If using ADI-2 for measurements, run it at 384k to get measurement compensation... ;)
 
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