How to do loopback test of DAC/ADC on macOS?

[Music1969]

Hi, I saw this loopback measurement of RME ADI-2 Pro and it did great:

https://www.audiosciencereview.com/...ment-of-rme-adi-2-pro-fs-black-edition.10834/

Can anyone share the software and steps required to do this with a DAC/ADC interface?

I especially want to get SINAD measurement @vitalii427

I have REW on macOS already.

Thanks!

 

[Music1969]

Specifically:

1. What software do I need. REW alone is enough?

2. What hardware do I need - just an XLR cable literally connecting analogue output to it's own analogue input?

3. What test signal file do I need?

4. What are some of the key setup requirements in REW

Thanks!

 

[mdsimon2]

Specifically:

1. What software do I need. REW alone is enough?

2. What hardware do I need - just an XLR cable literally connecting analogue output to it's own analogue input?

3. What test signal file do I need?

4. What are some of the key setup requirements in REW

Thanks!

1. REW is enough.

2. Yes, a XLR or TRS cable from analog output to input.

3. REW has built-in signal generator functionality.

4. You will need to set the RME as your input / output device in REW. Basic setup is output a 1 kHz tone using the generator and then use the RTA functionality to view the FFT. See link below for some good information on how to use the RTA functionality.

https://www.roomeqwizard.com/help/help_en-GB/html/spectrum.html

Michael

 

[Blumlein 88]

Yes, you can do the above with REW only. Some stereo interfaces will feedback if you put L out to L in and R out to R in. So you may need to feed L out to R in and R out to L in. If you have a multi-channel unit it usually won't matter.

You'll need to go under preferences and setup your sound card or interface. Take a look at that and see if you can get it to work, then if not maybe more specific questions can be answered. You want your sound card or recording interface chosen and you'll need to route signal in that interface to get them where you want, so knowing which interface you have might help us help you.

Then you can go into the Generator function and select a sine wave and what level you wish for it to have. Then open the RTA window to get the readout like you saw for the RME. Look thru the menus as one of the choices brings up the distortion panel. I'd be more specific, but I don't have MAC REW in front of me, and there might be little differences I'm forgetting.

Hopefully this will get you started in the right direction.

 

[Music1969]

Thanks @mdsimon2 and @Blumlein 88

Very helpful to get me started

 

[Music1969]

Yes, you can do the above with REW only. Some stereo interfaces will feedback if you put L out to L in and R out to R in. So you may need to feed L out to R in and R out to L in. If you have a multi-channel unit it usually won't matter.

You'll need to go under preferences and setup your sound card or interface. Take a look at that and see if you can get it to work, then if not maybe more specific questions can be answered. You want your sound card or recording interface chosen and you'll need to route signal in that interface to get them where you want, so knowing which interface you have might help us help you.

Then you can go into the Generator function and select a sine wave and what level you wish for it to have. Then open the RTA window to get the readout like you saw for the RME. Look thru the menus as one of the choices brings up the distortion panel. I'd be more specific, but I don't have MAC REW in front of me, and there might be little differences I'm forgetting.

Hopefully this will get you started in the right direction.

Hi guys

Some progress. I have something

How do I get the scale to show the peak signal at 0dBFS? Do I actually need to use a microphone to calibrate?

And what is the difference between red and black curves?

And anything else that you can see in my settings?

And how many seconds do you guys run the tone for in the RTA window? Until you see the averaging not changing anymore I guess?

Any help appreciated

 

[Music1969]

Ah I see the calibrate level.

So i just look at specs of max voltage (Vrms) of the interface XLR outputs right

And that is 0 dBFS

 

[Music1969]

Spec of analogue input of this interface is THD+N (1kHz at 0dBFS) = 0.0006 (SINAD 104 dB)

So I'm expect something around that or worse for loopback

 

[mdsimon2]

A few things that might help.

Check “Lock frequency to RTA FFT”.

On the graph if you move you cursor to the upper left corner you can change the scale from SPL to dBFS.

Can you click the gear in the upper right and show your settings?

Michael

 

[Music1969]

A few things that might help.

Check “Lock frequency to RTA FFT”.

On the graph if you move you cursor to the upper left corner you can change the scale from SPL to dBFS.

Can you click the gear in the upper right and show your settings?

Michael

Changed to 16 averages - I saw others had the same.

And dither 24 bits

And removed the red 'peak' curve

Still not sure how -5.8dBFS on the left correlates with -0.29 dBFS on the right

But the SINAD I'm getting is closer to manufacturers spec for their analogue input which is 104 dB at 0dBFS

 

[Music1969]

A few different input values. SINAD remains over 100dB (which is respectable?). Company spec is 104dB at 0dBFS

Still not sure how left window dBFS correlates with RTA window dBFS shown

 

[Music1969]

I had my interface sitting on a laptop cooler (vibrating fan) for the above measurements.

Turned the fan off and things look cleaner although SINAD didn't change much

Multitone not great but this is loopback not only D to A of course

 

[Music1969]

96kHz sample rate

20-20kHz vs 0 to 45khz . Not much difference, both close enough to the company spec for analogue input SINDAD

Not state of the art but their own spec of 104dB isn't claiming state of the art either

 

[Blumlein 88]

Well, looks like you are up and running on REW. Glad to see it. A few little things to figure out, but you by and large have it going.

 

[Music1969]

Well, looks like you are up and running on REW. Glad to see it. A few little things to figure out, but you by and large have it going.

Ha thanks.

What are some things that stand out above, that i need to work on ?

Also, is there any way to do IMD test to check for "ESS hump" using REW? Or not really?

 

[JohnYang1997]

Ha thanks.

What are some things that stand out above, that i need to work on ?

Also, is there any way to do IMD test to check for "ESS hump" using REW? Or not really?

Relatively difficult to produce the IMD vs Level graph. But you can test individual levels manually. Generator -> Two tone -> SMPTE 60hz + 7khz 4:1
set level to -35db and measure then -30db -25db -20db -15 db.

Also if you are using two devices you can open two instances of REW and use one as generator the other as analyzer.

 

[Music1969]

Relatively difficult to produce the IMD vs Level graph. But you can test individual levels manually. Generator -> Two tone -> SMPTE 60hz + 7khz 4:1
set level to -35db and measure then -30db -25db -20db -15 db.

Also if you are using two devices you can open two instances of REW and use one as generator the other as analyzer.

Thanks. Dither always 24bits? Or should be 16 bit?

IMD_DIN is the number to record for each level?

And is there any issue with the generator dBFS being 6dB lower than the RTA window dBFS?

Or RTA window dBFS is the only important one, going as close to 0dBFS as possible?

 

[JohnYang1997]

Thanks. Dither always 24bits? Or should be 16 bit?

IMD_DIN is the number to record for each level?

And is there any issue with the generator dBFS being 6dB lower than the RTA window dBFS?

Or RTA window dBFS is the only important one, going as close to 0dBFS as possible?

View attachment 112880

Maybe you can use Hanning window.
Dither 24bit or off should be fine.
It's normal to have lower level at 60hz because you have two tones now.

 

[Music1969]

Maybe you can use Hanning window.
Dither 24bit or off should be fine.
It's normal to have lower level at 60hz because you have two tones now.

Amir plots "SMPTE/DIN ratio" against input level.

Is that just the IMD_DIN number shown above, -47.9dB ?

 

[JohnYang1997]

Amir plots "SMPTE/DIN ratio" against input level.

Is that just the IMD_DIN number shown above, -47.9dB ?

Have you tried Hanning window?