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Do these measurements tell me anything?

exaudio

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#1
I've been a reader of ASR for awhile now and it's inspired me to try my hand at making some measurements. I have both a Topping D50 and a MiniDSP DDRC-24 and recently I came by a Yamaha MG10XU USB mixer that I thought I might be able to make some measurements with.

The Yamaha runs about $200 on Amazon, so I didn't expect a lot. But, since @amirm showed there's a significant performance gap between the D50 and the DAC portion of the DDRC-24 I thought I might be able to measure some differences between them. Instead, the FFTs I captured from both DACs looked nearly identical, which I presume is because its ADC isn't up to the task.

So, my question is this: If I haven't managed to measure the differences between the D50 and DDRC-24, what have I measured, if anything? Does it tell me anything about the Yamaha MG10XU other than it's probably not going to produce lab-grade measurements?

FFTs are 64k, Hann window, 4 averages. First up is the spectrum FFT of 1kHz tone at 0dBFS. The green is the DDRC-24 and the brown is the D50. As you can see from my, presumably flawed, measurements the FFTs look nearly identical.

Spectrum of 1kHz tone 0 dBFS MiniDSP DDRC24 vs Topping D50 (measured using Yamaha MG10XU & REW).png




The next measurement I tried was the jitter and noise "j-test" signal. I couldn't find it in REW's signal generator so I used @miero 's excellent post about Sox as a guide to generate my own j-test signal. In this plot the green is the D50 and the orange is the DDRC-24. Again both FFTs are very similar.

j-tests-d50-vs-ddrc24.png
 

Blumlein 88

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#2
Your measurements aren't flawed. It does appear your ADC is the limiting factor, and that both DACs perform better than the ADC.

The specs for the Yamaha show a - 1.5 db at 20 khz and looks like what you get. They also show a best distortion as -84 db which it appears you are actually getting better than that. So I believe you are correct the ADC is the bottle neck.

You could go to a higher FFT count even to 1 million and you might see some differences in the noise floors, but likely the ADC is shaping that more than the DACs as well. I also think Blackman_Harris 7 for the windowing is better than Hann for these purposes.
 
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