Measurements of Motu UltraLite mk4 (AKM DAC Version)

[March Audio]

OK, here are the results for the Motu Ultralite Mk4 with AKM DACs. Please note this was again in loopback and the ADC is not a good performance in this as the 8A, so its not really comparing apples with apples. I will use the 8A as the ADC to re perform the test tomorrow.

Note at -20dB on the FFT again very low IMD is shown.

 

[andreasmaaan]

OK, here are the results for the Motu Ultralite Mk4 with AKM DACs. Please note this was again in loopback and the ADC is not a good performance in this as the 8A, so its not really comparing apples with apples. I will use the 8A as the ADC to re perform the test tomorrow.

Note at -20dB on the FFT again very low IMD is shown.

These results do seem very strange. Your -20dB harmonic distortion test in post #1 shows harmonics at up to 107dB or so below the input signal, yet these apparently disappear completely in the two-tone test. Are you sure everything is set up correctly?

 

[March Audio]

Nothing I can see wrong. Remember it is a different A to D in the original measurements, but I would be upset if the QA was casing a lot of it sown distortion. Otherwise there is very little to set up. Check the input and output gains in the MOTU software, thats about it.

here is the arta result at -14dBFS from yesterday. 1st is about 110dB down.

This ia REW. 1st is about 112dB down. Note there is a different window, Kaiser v BH, and the averaging was much longer in the Arta measurement. Why the 2nd harmonic of the 60Hz is lthat much lower I dont know, but the rest of the data may not be very far out considering the different windows.

I will repeat tomorrow with the UL into the 8A and see what we get, but I would be very surprised if REW is messing things up

 

[Blumlein 88]

I don't see anything wrong with it just going by what is shown. It is surprisingly good. It also points a finger at the Quant Asylum.

I don't see any procedural mistakes in the results you posted.

Considering the low response at near max level, and dropping the test signal, it simply looks like a good result.

I don't think the SMPTE version is very revealing. You might do the twin tone 19+20 khz IMD at 5 db steps and see what that shows. It may show a similar pattern of reducing level greatly reducing distortion products.

 

[andreasmaaan]

I think I've just been confused by all the different measurements then.

It was this graph I was referring to when I said I thought it strange that no harmonics seemed to be present (or at least, no harmonics above the noise floor, which is 125dB below the signal):

 

[March Audio]

OK, I have checked through things again. I am happy with the results for the 8A, but I may have found an issue with the Ultralite results.

For those who are unfamiliar with this type of interface they have become extremely capable and sophisticated. They have mixers, effects like reverb and filtering all performed in on board DSP. They are essentially mini recording desks / studios. You can of course bypass all of this.

Below is the Motu interface. The input settings can control input gain from -96dB to +22dB. Output settings can control output volume over a range 0g -127dB to 0dB.

You have extensive signal routing, essentially you can send any input to any output via any effect or mixing along the way.

Mixing desk

It all might seem terribly complex but once you get used to it its fine.

Now back to the issue, I may have not had the settings set back to the simple "measure" parameters which is just in/out with no other processing. A mixer fader may have reduced the output level. However hopefully all this will do is move the level of the lowest IMD. It would explain the different harmonic distortion levels from the original measurement.

Second issue. In the original measurement I discussed the spray of harmonics at high level which was disappointing. It looked like amp clipping, which is exactly what it is. With both the input and output gain settings at 0dB both input and output clip.

With a fixed output DAC this would be horrendous, but thats not what this is. We can legitimately change the gain of the input and output amps turn the volume down!

It appears that the output needs to be set to -1dB and input set to -2dB to prevent clipping with a looped back 0dB input signal. See below. Basically Motu have screwed up the gain settings on the amps. The output set to 0dB should not clip. To be clear this is an output voltage of 5.980 V RMS (balanced) and half that single ended. Way above the normal domestic voltage of 2 V rms. This is probably not to be considered any issue for the input as when recording you would always monitor the input level on a VU meter anyway.

I dont think its "cheating" to run the output and input at slightly reduced levels as being variable is part of their normal function. Its just annoying that something simple like this could cause problems if you dont know about it.

Note that this is the old version of the Ultralite mk4 with AKM DAC chips. Its going to be interesting to see if the new version with ESS Sabre dacs has the same issue. The 8A doesnt appear to suffer this issue.

 

[Blumlein 88]

Yes, you have to watch out for those kind of things. As the interfaces get so capable it is easy to overlook.

In my Zen Tour, the basic noise floor of the front panel line inputs is several decibels lower. However, the noise floor gets modulated by the signal. Not as much as the Quant appears to, but some few decibels. The Line inputs on the rear aren't modulated at all. They also are of several decibels lower distortion. So one has to keep an eye on many things to get the most out of these. In context of what all it is capable of doing, I would NOT consider lowering level by 1 db and 2 db cheating. You are just adjusting for best possible performance.

EDIT: added NOT in the above post as was my original intention. Sorry.

 

[March Audio]

OK, I have re-run the IMD test using the Motu 8A as the ADC with the output of the Ultralite mk4 (AKM version) turned down by 1dB to prevent clipping.

The better ADC in the 8A is evident here and IMD has reduced over the original measurement made by the Ultralites ADC. Not really a surprise.

At the sweet spot of -20dB the IMD is only just above the noise floor. So I beleive the results.

Just need to check with @amirm to ensure there isnt something fundamentally different about our tests to invalidate the comparison.

Regarding testing, I am going to be sticking with the 8A as an ADC. The QA401 noise floor issue is a PITA.

 

[March Audio]

Just for completeness I have also run the DIN and CCIF tests. For those unfamiliar the SMTPE is two tones, 60Hz and 7kHz with a 4:1 amplitude difference. The DIN is similar but tones at 250Hz and 8kHz, again 4:1 amplitude. In the tests the 60Hz will modulate the 7kHz (250Hz the 8kHz) and appear as sidebands around it at 60Hz and 250Hz respectively. The CCIF test is two tones at 19kHz and 20kHz at 1:1 amplitude. This will generate a difference tone at 1kHz and sidebands of 1kHz around the fundamentals. This result will look different to the other two tests.

DIN

CCIF

The SMTPE and DIN tests basically overlay each other. The CCIF generates a different characteristic.

 

[March Audio]

@Blumlein 88
I know you have measured your interfaces previously. Any chance of performing the IMD test?

Latest REW is here

https://www.avnirvana.com/resources/

and attached is my excel file

 

[Blumlein 88]

Yes. It may be a couple days.

 

[March Audio]

In context of what all it is capable of doing, I would NOT consider lowering level by 1 db and 2 db cheating. You are just adjusting for best possible performance.

EDIT: added NOT in the above post as was my original intention. Sorry.

Haha you did a Trump ! Difference being I believe you

 

[Blumlein 88]

I did have some files of the Focusrite Forte where I have done 14 khz and 15 khz at -20 db. The 1 khz difference was .00008% which appears to be mostly noise. It may be elevated 3 or 4 db from the surrounding frequencies. 128 K fft.

I also had a file of 18khz and 19 khz at -60 db. The 1 khz level was the noise level which was -148 db with 128 k FFT. Which works out to about .004%, or 88 db below the signal level. This definitely was just noise. So the real amount of IMD was below the noise floor.

I'll do the equivalent to your tests when I get a chance in a couple days and fill in the other levels. Your results look quite believable.

Also the Marantz AV preamp, on the -20 db 14+15 khz test had a value of -101db vs the signal level. Or about .009%.

 

[andreasmaaan]

Nice one @BE718! Results are still very impressive.

 

[Blumlein 88]

@BE718
I did get some measurements done for you today. Using REW. Takes a while vs what I usually do. I'll get the results back to you in the spreadsheet soon.

Looked just a bit at the Virtins software on the trial. Ran into multiple first world problems.

Problem #1, the update to the Launcher for my Antelope audio device doesn't work. So I couldn't use it. I had it working on Mac, but hadn't bothered with the windows update till today. They sort of don't give you a choice. Still works on my Mac though it too was very problematic to get working last month. Antelope is trying really hard to sour me on a really nice product which is set up in a way I just love. Much more of this though and it will get sold down the road. The worst is many, many people are having similar problems and Antelope isn't dealing with it well. There is some basic issue with what they are doing.

I hooked up my Forte and my 18i20. Both from Focusrite. Which use a driver in each case called Focusrite USB 2.0 Driver. The software could differentiate between the two devices, but seems to use one or the other for ADC or DAC, but you can't separate them or I didn't figure it out. I could look at noise floors. They look about like what I get with my own testing.

 

[March Audio]

Dont know if this will help but you can use ASIO and MME at the same time for ADC and DAC. It might separate them then.

 

[Olli]

@March Audio: Any chance you'll give us an update on how the MOTU UL MK4 ESS Version measures?

 

[March Audio]

At some point, but I'm a little busy ATM.

 

[Olli]

Thanks. Much appreciated. And looking fwd to the reviews of you power amps. Sounds promising!

 

[777]

MarchAudio, can you telling me please, how you did the jitter measurement with QA401 ? Which is it the protocol ?