Loopback measurement of RME ADI-2 PRO FS (Black Edition)

[vitalii427]

 

[netcipher]

Just look at the overall values so that's 114dB v 122dB.

I think that was a 512k fft.

I did not pay attention, since the interface does not indicate that it is the SNR.

 

[Rja4000]

Wow! That is not subtle difference definitely

Theory says 9dB for SNR.
That's about what we see here.
Story may be very different for THD+N though.

 

[Matias]

What happens if we take the parallel thing to an extreme? Add 12,18, 24 channels of a pro interface? Would it lower distortion and noise floor to APx555 levels?

Example: 8 channels per Focusrite Scarlett 18i20 3rd gen for 500usd each. They can be Daisy chained. Say we use 3 for 1.500usd and add all 24 channels, how would it measure?
https://www.amazon.com/Focusrite-Scarlett-18i20-Audio-Interface/dp/B018W7BW36/

 

[March Audio]

What happens if we take the parallel thing to an extreme? Add 12,18, 24 channels of a pro interface? Would it lower distortion and noise floor to APx555 levels?

Example: 8 channels per Focusrite Scarlett 18i20 3rd gen for 500usd each. They can be Daisy chained. Say we use 3 for 1.500usd and add all 24 channels, how would it measure?
https://www.amazon.com/Focusrite-Scarlett-18i20-Audio-Interface/dp/B018W7BW36/

Noise should keep going down distortion will not. You also may start running into issues with the input impedance dropping

 

[PierreV]

What happens if we take the parallel thing to an extreme? Add 12,18, 24 channels of a pro interface? Would it lower distortion and noise floor to APx555 levels?

Example: 8 channels per Focusrite Scarlett 18i20 3rd gen for 500usd each. They can be Daisy chained. Say we use 3 for 1.500usd and add all 24 channels, how would it measure?
https://www.amazon.com/Focusrite-Scarlett-18i20-Audio-Interface/dp/B018W7BW36/

Whatever level of improvement you get by going to 1 signal vs averaging 4 signals, you should be able to get again by averaging 16 signals and so on. The square root rules, at least in theory and on random noise but, of course, there can be a lot of non-random stuff sneaking in too...

 

[MC_RME]

If you want to use the RME as a measurement device, you can get higher performance by either using the balanced phone output, either directly summing the XLR outputs by using Y cables in mono mode (I didn't try this later one, but @MC_RME said that's how he's proceeding himself).

IMHO the correct sentence should have been:... you can get higher performance by either using the balanced phone output, or directly summing the XLR outputs by using Y cables into mono mode.

Just to avoid confusion.

And March is right, THD usually stays at the worst one of the multiple channels, while noise goes down a lot. The hardware channel averaging is quite handy as you immediately get valid numbers like noise floor RMS etc. And you can still FFT average to go more deep again...

 

[L0rdGwyn]

There is a forum member with the M4. Measures will be forthcoming I do believe.

Correct, I will put some measurements up this week, see if I can get to it today.

 

[JohnPM]

"Lock frequency to RTA FFT" makes better results and almost no skirt

When locked to the FFT length you should be able to use the rectangular window to eliminate any spreading. Otherwise better using Blackman-Harris 7 or Dolph-Chebyshev 200 than Hann.

 

[vitalii427]

When locked to the FFT length you should be able to use the rectangular window to eliminate any spreading. Otherwise better using Blackman-Harris 7 or Dolph-Chebyshev 200 than Hann.

Thanks!

 

[L0rdGwyn]

Here are the MOTU M4 loopbacks: https://www.audiosciencereview.com/forum/index.php?threads/motu-m4-loopback-measurements.10890/

 

[Hee]

나는 motu 828es 루프백


thd + n : main out -1db, 0db의 줄 (기본값) = best

동적 범위 : main out 0db (full vol), + 1db 라인 = 최고

rmaa 루프백 : main out -2db, 0db 라인

828es는 좋다! ^ _____ ^

 

[exaudio]

IMHO the correct sentence should have been:... you can get higher performance by either using the balanced phone output, or directly summing the XLR outputs by using Y cables into mono mode.

Just to avoid confusion.

And March is right, THD usually stays at the worst one of the multiple channels, while noise goes down a lot. The hardware channel averaging is quite handy as you immediately get valid numbers like noise floor RMS etc. And you can still FFT average to go more deep again...

@Rja4000, @MC_RME, @March Audio, I'm trying to understand your setup for summing/averaging measurements from multiple channels. I assume the cabling looks something like this:

Do I have that right? Also, @MC_RME mentioned setting the ADI-2 Pro in mono mode. I'm assuming that by recording in mono the device mixes/sums the two input channels down to one (after the conversion to digital?). And @March Audio must be able to do that with his Motu so that all 8 channels are mixed down to one? If my ADC doesn't have a mono mode is there a way to get REW's RTA tool to average the input from two channels?

 

[MC_RME]

The quoted sentence refers to the output mono summing by using a simple 2 x XLR F to 1 x XLR M. This works a treat with RME devices, most probably many others as well, but for these I can't guarantee it. On the input side your drawing is correct and would use a 1 x XLR F to 2 x XLR M. Those cables are available online at low prices. The two input signals then must be summed and reduced in level by 6 dB. In the ADI-2 Pro the input option 'M/S Processing' does that, so the software can be used on input channel 1 without further modifications.

 

[Rja4000]

Those cables are available online at low prices.

I use those cables
https://www.cordial-cables.com/en/products/cfy-fmm
https://www.cordial-cables.com/en/products/cfy-mff
Wiring is described.

On the DAC side, this is one way to do.

You average both channels of one of the DAC outputs.
The RME ADI-2 pro has 2 stereo DAC outputs.
(The RME ADI-2 DAC has 1)

The other way is to use front-panel balanced phone outputs.
Each channel (L R) is then a sum of that channel from both stereo DAC outputs.
The benefit is that you may push the level to +28dBu.
The drawback is that you don't have +4dBu, +19dBu and +24dBu ranges available.
Just +13dBu (low gain) and +28dBu (High gain).

 

[Rja4000]

The other way is to use front-panel balanced phone outputs.

Note that you can NOT directly sum the 2 balanced phone output channels by using an Y cable.
If you do, you'll get a message saying that the protection was activated to prevent a short on the output.

 

[vitalii427]

@MC_RME, Is there any way use 4 separate output channels over USB?

 

[MC_RME]

Use the Multi-channel mode (6 In 8 Out).

 

[vitalii427]

Use the Multi-channel mode (6 In 8 Out).

Oh, thanks!
I should read the manual carefully

 

[Rja4000]

I just performed some measurements on the RME ADI-2 Pro fs in loopback mode for the various methods:

RME ADI-2 Pro fs Loopback @4Vrms
Output and input +19dBu range
Balanced Y Cable on both outputs (Main out)
Balanced Y Cable on both inputs and M/S mode

SINAD = 112dB


RME ADI-2 Pro fs Loopback @2.5Vrms
Output and input +13dBu range
Balanced Y Cable on both outputs (Main out)
Balanced Y Cable on both inputs and M/S mode

SINAD = 114dB


RME ADI-2 Pro fs Loopback @2.5Vrms
Input +13dBu range
Output Balanced Phone mode - Low gain (+13dBu)
Balanced cables of both channels to each input
(So NO output sum)
RME input in M/S mode

SINAD = 115dB !


I also received today my Linear Audio Autoranger II

RME ADI-2 Pro fs Loopback through Autoranger II @4Vrms
Autoranger in 1V output mode
RME Output +19dBu range @4Vrms
RME Input +4dBu range
Balanced Y Cable on both outputs (Main out) to Autoranger Balanced in
Balanced Y Cable from Autoranger Balanced out to both RME balanced inputs and RME input in M/S mode

SINAD = 110dB
or 2dB loss vs direct RME loopback


RME ADI-2 Pro fs Loopback through Autoranger II @2.5Vrms
Autoranger in 1V output mode
RME Output +13dBu range @2.5Vrms
RME Input +13dBu range
Balanced Y Cable on both outputs (Main out) to Autoranger Balanced in
Balanced Y Cable from Autoranger Balanced out to both RME balanced inputs and RME input in M/S mode

SINAD = 110dB

All this means the loopback SINAD for the Autoranger II alone should run somewhere between 112dB and 123dB...
Should be good enough to perform basic measurements on speaker amps.