Audio measurement gear

[Blumlein 88]

Hi
I'm trying different softwares.
Tried Mi Pro, Hpw-works, SpectraPlus and a few others.
My goal is to be able to assess my ADCs and ADCs (Hi level).
For that, I want to be able to compare it to RME ADI-2 Pro FS as a reference.
That means 2 ASIO drivers with separate channels.
As an example, send to the RME analog Left and SPDIF right, while input is set to RME Analog L+R
Then I can loop back the RME, while evaluating another DAC fed by the SPDIF.
The 2 software's I end up with are Mi Pro and HPW-Works.
The later, I can't evaluate fully, since trial is hard limited...
And I don't see how I could automate it.
But Mi Pro gives me very different IMD figures.
There is 10dB difference between Spectra Plus and MI Pro regarding IMD.. and Amirm is publishing still other figures, while everyone seem to align on SMPTE IMD (60Hz+7kHz)

Any idea why?

First eval: my Motu 828mk3 is performing approx. 10dB worse than the RME.
Both for ADC and DAC, whatever software is used.

Maybe more detail for distortion would be helpful.

I prefer 19+20khz for IMD (CCIF).

Maybe it isn't as automated, but I've gotten consistent results using a few approaches. You might try REW, which can be used quite nicely for electronics. You can do IMD, or single tone or sweep measures with each harmonic displayed. It is free as well. Doesn't do as much as some of the software you mention, but maybe it would answer basic questions about Motu Vs RME as a start.

SIY suggested Virtins Multi-instrument which is very capable. I don't think it will allow two pieces of gear on Windows. So you'll need two computers. In any case, he wrote a review of it here:

https://www.audioxpress.com/article/practical-test-measurement-the-virtins-multi-instrument-software

 

[MC_RME]

For that, I want to be able to compare it to RME ADI-2 Pro FS as a reference.
That means 2 ASIO drivers with separate channels.
As an example, send to the RME analog Left and SPDIF right, while input is set to RME Analog L+R
Then I can loop back the RME, while evaluating another DAC fed by the SPDIF.

Why does that need 2 ASIO drivers? The ADI-2 Pro wil send the stereo playback signal via analog and SPDIF output simultaneously...

 

[Rja4000]

Why does that need 2 ASIO drivers? The ADI-2 Pro wil send the stereo playback signal via analog and SPDIF output simultaneously...

Sorry, I explained that badly.
The constraint is that I want to mix analog left and spdif right, as an example, to be able to compare the RME ADC to another one on the same view (say, left channel RME and right channel 'other', fed back in RME through SPDIF in)
ASIO selection shows RME Analog and Spdif as 2 separate output or input lines. So when a software only allow one i/o line for input or output, I can't mix them.

 

[Rja4000]

Maybe more detail for distortion would be helpful.

I prefer 19+20khz for IMD (CCIF).

Maybe it isn't as automated, but I've gotten consistent results using a few approaches. You might try REW, which can be used quite nicely for electronics. You can do IMD, or single tone or sweep measures with each harmonic displayed. It is free as well. Doesn't do as much as some of the software you mention, but maybe it would answer basic questions about Motu Vs RME as a start.

SIY suggested Virtins Multi-instrument which is very capable. I don't think it will allow two pieces of gear on Windows. So you'll need two computers. In any case, he wrote a review of it here:

https://www.audioxpress.com/article/practical-test-measurement-the-virtins-multi-instrument-software

Thanks.
I will try REW and 19k+20k.
I've done the SMPTE 60Hz+7kHz to be able to compare with Amir's measurement (and his figures are lower)

What I call 'Mi pro' is Virtins Multi Instrument and it works with one single PC.

 

[Blumlein 88]

Thanks.
I will try REW and 19k+20k.
I've done the SMPTE 60Hz+7kHz to be able to compare with Amir's measurement (and his figures are lower)

What I call 'Mi pro' is Virtins Multi Instrument and it works with one single PC.

REW also will do the SMPTE IMD tone as well.

 

[Rja4000]

REW also will do the SMPTE IMD tone as well.

Hi
I gave it a try.
Indeed, REW also works pretty well.
(IMD figure for SMPTE tones is labelled IMD DIN, but I guess that's the same)
The help is also very... helpful.
But now I have still another measurements set, different from the others.

That makes me wonder if Amir could check those tools versus what he gets with the AP and explain which setting is giving closest figures...
?? Any chance ??

 

[amirm]

That makes me wonder if Amir could check those tools versus what he gets with the AP and explain which setting is giving closest figures...
?? Any chance ??

I can test the generator in these tools to see what they do. The analyzer part would depend on sound interface used and such.

On REW, JohnPM can advise but I think it uses a window into impulse response which separates the distortion. Alas, of there is overlap with the signal itself, the resulting analysis would not be correct.

 

[Blumlein 88]

Hi
I gave it a try.
Indeed, REW also works pretty well.
(IMD figure for SMPTE tones is labelled IMD DIN, but I guess that's the same)
The help is also very... helpful.
But now I have still another measurements set, different from the others.

That makes me wonder if Amir could check those tools versus what he gets with the AP and explain which setting is giving closest figures...
?? Any chance ??

So how different are your REW results from Amir's on the RME? The ADC on the RME isn't equal to what is on the AP. And I don't recall whether Amir ever measured the ADC side.

I could check, but at least doing loopbacks or separate DAC to ADC tests my results in REW were pretty much exactly what I get doing the test manually. Manually is to send in a pair of tones a fraction of a db below max, and record it. Then analyze the result with Audacity or WaveSpectra using FFT's.

I'm guessing, but as Amir said above, the fellow behind REW posts here and we could ask, but I assume he does what I do with sweeps and distortion. If I match the sweep rate with the size of the FFT, you can get results that are essentially identical to doing single tone spot checks. And with the IMD tests you aren't using a sweep anyway.

 

[Rja4000]

Hello

Here are some measurements of the RME ADI-2 Pro FS in Loopback mode with REW
Main output 1/2 L to Analog In L, XLR I/O, set to +19dBu
24 bits, 48kHz
Output -4.7dBFS = +14,3dBu = 4.05Vrms (approx.)

THD + N @997Hz 4V

IMD SMPTE @4V

IMD SMPTE @ -30dbFS

IMD SMPTE @ -60dBFS

IMD CCIF @ 4V

Jitter test (Square wave @ 12kHz 0dBFS)

THD with 1/3 Octave sine @ -10dBFS

Distortion HD2 & HD3 vs Frequency (Bandwidth 20kHz)

(By the way, the stepped line is fine, but the results disappear after it's finished)

Not too bad for a DAC+ADC loopback...

My main question is about IMD measurements, which are significatively different (better) than Amirm's trend for the DAC alone.
As I think this trend is most useful, I'm interested to duplicate it...

By the way, is there a way to automate the linearity measurement with REW ?

 

[Blumlein 88]

Looks like good results on the loopback. Not terribly off from Amir's. Maybe a touch more noise, similar harmonic distortion. Maybe better IMD.

I don't know of a way to automate the linearity measurement in REW, but maybe more creative people can come up with one.

I use a test signal that isn't the same as the one used by AP. I use a quarter sample rate tone because all sample values should be 0 or plus or minus an exact bit at levels in steps of one bit size. I use a -60 dbFS reference tone at 1 khz. Follow it with bit levels 10 thru 24. So the info isn't continuous, but does show if each single bit level is the right size. It was tedious to make up with exact values, but if you wish I could send you a copy.

I record that signal, digitally adjust the result so the reference tone is exactly -60 dbFS which lets me see what levels were output by the DUT.

 

[Rja4000]

I use a test signal that isn't the same as the one used by AP. I use a quarter sample rate tone because all sample values should be 0 or plus or minus an exact bit at levels in steps of one bit size. I use a -60 dbFS reference tone at 1 khz. Follow it with bit levels 10 thru 24. So the info isn't continuous, but does show if each single bit level is the right size. It was tedious to make up with exact values, but if you wish I could send you a copy.

I record that signal, digitally adjust the result so the reference tone is exactly -60 dbFS which lets me see what levels were output by the DUT.

That looks interesting, but I'm not sure to understand you.
Could you describe a bit more ?

By the way, I received a message from the author of HPW-Works, following a question from me, and he recommends to use the RME in "double balanced phone" mode, since it will then use a separate DAC for each channel and should be 3dB better.
I'll give it a try and publish the results too.

Still, my figures for IMD are very different vs the results Amir had with the DAC, with his "IMD graph", and I don't understand why.
@Amir: Any idea ?

Maybe I should create a new topic for that?

 

[Rja4000]

Here is a measurement with "Balanced Phone" mode
(Phone 3/4=Left channel)

This is still the RME ADI-2 Pro FS loopback, so DAC+ADC
THD+N 111.6dB,
N+D 112.4dBA

Note that this is for 12.31 Vrms here
(0dBFS=28dBu, but as Analog input is max +24dBu, I lower the output by 4dB on the RME itself)

 

[Rja4000]

Pretty close from Amir's measurement of RME ADI-2 DAC FS:

Bellow chart copyright of Amir
I repost it here to avoid you spending time looking for it

 

[Rja4000]

Best result I could get here:
Still in "balanced phone" mode, if I dial down enough on the RME level, the output switches to Low power mode.
Then the input can be set to +13dBu range.

Here is a measurement with RME level set at -17dBFS, which is +11dBu output (2.7Vrms)
That's -113dB for THD+N (-116dBFSA N+D)
And this is still both DAC and ADC.

 

[Blumlein 88]

That looks interesting, but I'm not sure to understand you.
Could you describe a bit more ?

For 48 khz I use a 12 khz signal. Here is one using only the 10th bit. A level of -60.21 dbFS Notice you only have either a zero or plus or minus value and I've arranged it so we don't have multiple bit levels to make the signal by using 12 khz. So if I use this signal the DAC is only being asked to output using a single bit level.

Here is the same thing only for the 16th bit.

Now if I do this using regular line inputs, I'll need something with incredibly low noise levels to see the actual level of 20-24 bits (minus 120-144 dbFS). Now if you have an FFT with enough bins you can probably see those low levels. Even then it will be tough to see it mixed in with the noise of your measuring device below 20 bits. So one other thing I do is feed the DAC output into a microphone preamp. The highest signal is -60 dbFS which with most DACs having a 2 volt max output will be low enough it won't overload a microphone preamp. The microphone preamp can apply analog gain. The advantage is I can add 60 db of gain, which pushes the signal and the noise up in level, but this puts the noise level of the device well above the noise level of my preamp and ADC. So they become a non-issue and I can see the actual noise and signal levels of the DUT. Even if the DAC being tested has 120 db of dynamic range I'm only looking at the lower 60 db which will fit into the range of my preamp and ADC easily.

So I have my amplified recording of the bit levels from the 10th thru the 24th bit. Which is why I put the -60 dbFS reference tone in. I now digitally reduce the level of that tone until it is back at -60 dbFS and everything else is in proper proportion in the recorded test signal. Micrphone preamps usually have better EIN specs than line level inputs. The RME may be quiet enough you don't need this extra step to see linearity at lower levels.

In any case here is a spectrogram screen shot from a March Audio DAC for low level linearity. The upper is into the line level inputs and the lower via the microphone inputs with level adjusted afterwards. You can see the lower noise floor in this spectrogram which goes to light gray at -150 dbFS. If you look carefully the lower one shows the 23 rd bit and a hint of the 24th. The vertical bars are just markers following the 16th bit, 20th bit and 24th bit.

I took a 16k FFT of the lower file above for the 23rd bit. Dumped the results into a spreadsheet. Hz on left level in db on the right. You see a value of -138.62 db measured at 12,000 hz and the exact value should have been -138.47 db. So pretty close.

I hope this made sense. If not, ask more questions.

 

[wynpalmer]

Hello

Here are some measurements of the RME ADI-2 Pro FS in Loopback mode with REW
Main output 1/2 L to Analog In L, XLR I/O, set to +19dBu
24 bits, 48kHz
Output -4.7dBFS = +14,3dBu = 4.05Vrms (approx.)

THD + N @997Hz 4V

View attachment 29985

IMD SMPTE @4V

View attachment 29986

IMD SMPTE @ -30dbFS
View attachment 29987

IMD SMPTE @ -60dBFS
View attachment 29988

IMD CCIF @ 4V
View attachment 29989

Jitter test (Square wave @ 12kHz 0dBFS)
View attachment 29990

THD with 1/3 Octave sine @ -10dBFS
View attachment 29991

Distortion HD2 & HD3 vs Frequency (Bandwidth 20kHz)
View attachment 29992

(By the way, the stepped line is fine, but the results disappear after it's finished)

Not too bad for a DAC+ADC loopback...

My main question is about IMD measurements, which are significatively different (better) than Amirm's trend for the DAC alone.
As I think this trend is most useful, I'm interested to duplicate it...

By the way, is there a way to automate the linearity measurement with REW ?

Could you please specify the configuration/settings for the loopback test?
I'm having difficulty duplicating your results with REW and my ADI-2 PRO FS.
Thanks!

 

[Rja4000]

Could you please specify the configuration/settings for the loopback test?
I'm having difficulty duplicating your results with REW and my ADI-2 PRO FS.
Thanks!

Hello
What do you want to know ?

Loopback mode with REW:
- Main output 1/2 Left is connected to Analog In Left with an XLR-XLR cable,
- Both Output and Input are set to a range of +19dBu
I measured with a multimeter to make sure that the Output set to -4.7dBFS (which is +19dBu-4.7dBu=+14,3dBu) was 4.05Vrms (approx.)
(I wanted 4V to duplicate Amir's conditions.)

Everything else is visible in the screenshots and can be replicated easily with REW.

By the way, in "Phone Balanced mode", output from front Phone 3/4 sent to XLR Input, with a 1/4" Jack TRS to XLR cable, gives even better results, if done with Output set to Lo Power, and input set to +13dBu.
This is because both channels of one DAC are used to feed one input channel. (The Pro has 2 stereo DACs) (as per RME data)

 

[wynpalmer]

Hello
What do you want to know ?

Loopback mode with REW:
- Main output 1/2 Left is connected to Analog In Left with an XLR-XLR cable,
- Both Output and Input are set to a range of +19dBu
I measured with a multimeter to make sure that the Output set to -4.7dBFS (which is +19dBu-4.7dBu=+14,3dBu) was 4.05Vrms (approx.)
(I wanted 4V to duplicate Amir's conditions.)

Everything else is visible in the screenshots and can be replicated easily with REW.

By the way, in "Phone Balanced mode", output from front Phone 3/4 sent to XLR Input, with a 1/4" Jack TRS to XLR cable, gives even better results, if done with Output set to Lo Power, and input set to +13dBu or +19dBu.
This is because both channels of one DAC are used to feed one input channel. (The Pro has 2 stereo DACs) (as per RME data)

That's all that I need. I now get essentially identical results to the ones that you posted.
Thank you very much.

 

[wynpalmer]

I just used the combo to test a home made phono preamp.

Not a balanced input, MC with 63dB of gain , 10 ohm source impedance, +19dBu input setting for the RME- 60Hz is down 16dB from the above level with the phono cables removed.
The ADI-2 PRO FS is indeed a remarkable device.

 

[Rja4000]

The ADI-2 PRO FS is indeed a remarkable device.

I agree.

Just gave Virtins Multi Instrument a try:

OK, -100dB doesn't make sense...

But that's still -66.8dB for IMD SMPTE @ -60dBFS
That's coherent with REW above.

And that's what I don't understand:

Here is Amir's result for the ADI-2 DAC (copied from his review)
Thats -51dB or so for the same -60dBFS.
How I could I measure 15dB better ???