Review and Measurements of RME ADI-2 DAC

[watchnerd]

Excuse me? WASAPI is in general, flawless and bit-perfect. I don't get people's obsession with ASIO. That it doesn't work with all sample rates with the RME ADI-2 DAC is rather an exception as confirmed by their customer support and has nothing to do with "poor quality" so there's no reason to call it so (unless you have proof that ASIO is in fact superior?).

Secondly, Amir has in fact stated that ASIO drivers are necessary for flexible functioning.



Others have reported that under OSX that there are no problems.

I use the Pro with OSX and it doesn't have this problem.

 

[amirm]

Thank you for this review. Have you also measured THD+N vs frequency?

Yes, but had forgotten to post it . Here it is:

As we see, above 40 Hz, it is best in this class.

 

[Dro]

Thank you. Any idea why it is so "high" below 40 Hz?

 

[SIY]

Interesting. I did not see the same amount of LF rise in distortion. What do you think causes that?

 

[amirm]

Thank you. Any idea why it is so "high" below 40 Hz?

No, but seems to be related to its much higher output. See the next test where I run it at -10 dB and distortion is then a flat line.

 

[amirm]

So here are the results of an interesting test prompted by a paper by Benchmark Media: https://benchmarkmedia.com/blogs/application_notes/12838141-headphone-amplifiers-part-1

In a nutshell, it says that real headphone loads substantially increase the distortion of the amplifier versus dummy/resistive loads. Here is the example they give of their headphone amp and that of two other unknown units:

With dummy load:

With Sony MDR-V6 headphone:

We see that their line in navy blue at the bottom does not change. The distortion profile of the other two amplifiers change a lot.

Here is my version of that test, with a 150 ohm dummy load, volume set to -10 dB on front panel (to keep the headphones from being damaged) and four different headphones including the MDR-V6:

Starting with 150 ohm dummy load in cyan, we see that the distortion profile is pretty flat now unlike the max volume that showed a rise in low frequencies.

When we change the load to headphones, the distortion profile wildly changes unfortunately. So there is some secret sauce in Benchmark headphone amps that the RME does not have.

Based on running this test on other headphone amps, the HifiMan HE400i seems to cause least amount of variations. It is essentially the same as dummy load in mid-frequencies where our hearing is most sensitive.

The grado is brutal, causing such large swings. Looking at its impedance curve does give much clues to this variation: https://www.innerfidelity.com/images/GradoSR60i.pdf

Comments?

 

[SIY]

What does that drive level correspond to in terms of SPL? The distortion seems suspiciously high.

 

[amirm]

What does that drive level correspond to in terms of SPL? The distortion seems suspiciously high.

It is 3 volts RMS output. To convert that to SPL you have to look at the real efficiency of the headphones and impedance at each frequency.

I can tell you it is exceptionally loud. My Grado sounds like a speaker playing the tone from a distance of 3 feet!

 

[Dro]

If a headphone itself produces a lot of THD, would you not be able to measure it with your test, as the driver converts the mechanical to electrical energy? No idea why Benchmark amps are allegedly immune to that though.

Edit: 3 V RMS would be around 120 dB SPL with the SR60i. You can see the Grado's distortion goes up with increasing SPL at low frequency.

 

[mindbomb]

@amirm

How does the topping amp handle these headphones? does the 10 ohm resistor make things a lot worse? or does it help?

Also, I'm surprised the hifiman isn't flat. I thought planar magnetic headphones were supposed to be like resistors.

 

[amirm]

I am not measuring the output of the headphones. I am measuring the distortion at the connection to the headphones. So it is the increased distortion of the amplifier due to real load that the headphones put on it.

Here is a useful note from Benchmark on low frequency rise on distortion:

 

[SIY]

I can tell you it is exceptionally loud. My Grado sounds like a speaker playing the tone from a distance of 3 feet!

Yow! I was wondering if this was a mechanical bottoming phenomenon. That might not please an amp... I unfortunately had to give the RME setup back, so I can't go back and redo the test with an actual headphone, but I may try this with one of the other headphone amps I have on hand.

/looks for cheap headphones whose loss won't cause crying

 

[Dro]

@amirm could you redo this test with the Grado at a lower level? Say -30 dB rather than -10 dB.

 

[Blumlein 88]

One would think it is a damping thing with the output impedance and possibly current supply into reactive loads.

 

[Gridlock]

Hi. I just wanted to confirm that under Linux this dac has no problem with all sample rates. I had a problem with coax spdif at 192khz with an auralic aries le which appeared to be because the voltage wasn't high enough, all the other sample rates worked fine though. When I tried the aes output of the aries with a neutric aes - bnc converter into the spdif input with a bnc to phono cable it worked fine. Auralic thought that the voltage was higher on aes which helped. Absolutely no problems with usb though, all of our Linux computers have no problems with all sample rates being detected and changed automatically. Overall fantastic dac!

 

[amirm]

@amirm could you redo this test with the Grado at a lower level? Say -30 dB rather than -10 dB.

I ran it at 1 volt RMS which corresponds to -19.5 dB on RME scale. This time the Grado reproduced the lows without bottoming out. Here are the results:

Looks more or less the same. The higher frequencies now have more noise so the distortion is swamped in there.

 

[amirm]

@amirm

How does the topping amp handle these headphones? does the 10 ohm resistor make things a lot worse? or does it help?

Definitely worse:

Had to lower the top of the graph by some 25 dB to keep it all visible.

 

[amirm]

And here is the same data for Auralic Gemini 2000 @1 volt output:

The baseline (dummy load) is worse than Topping but with real headphones, performance is better.

Another conclusion seems to be that the order does not change. The HiFiman HE400i is least stressful on the DAC and Grado is the worst.

 

[Dro]

Thanks. Could you also measure the IEM output?

I presume you don't have any Benchmark headphone amplifier lying around?

 

[Veri]

Love these real-world headphone tests amir. I really wonder about Benchmark's claim that their amp does better.