He is not understanding the nature of this analysis. I am trying to replicate both noise floor and distortion in Rob's posted measurement. Here is what Rob says above his posted graph:
https://www.head-fi.org/threads/chord-electronics-dave.766517/page-10#post-11721177
"But around October 2014 AP launched the APX555, and this had a clever system to enable more accurate measurements of distortion and noise floor. What this instrument does is the employ two ADC's per channel, and an automatic notch filter, so one ADC uses notched out fundamental, and another ADC for the fundamental. The instrument then stitches the two plots together in the digital domain.
It also had a very high purity analogue oscillator - the system has residual THD at 2.5v of -150dB. Since I need a high purity analogue source to test the pro ADC project, and since Dave at that time exceeded the old AP measurement capacity, once AP launched the APX555 I went out and purchased one.
So we can now see the performance of Dave using the APX555:"
The bolded statement is the High Performance Sine Analyzer feature. If you don't enable it, the ADC in AP will create its own harmonic distortion, substantially corrupting the measurements of high-performance audio devices.
Here is the performance of DAVE with and without HP Sine Analyzer in AP:
View attachment 229171
As you see on the right, distortion spiked are now in -138 dB category -- far from -150 dB that Rob showed in his measurement:
Notice how there is a "skirt" under the 1 kHz tone in Rob's measurement, matching mine when using HP mode of the AP. So HP mode has to be used with the signal present. It then reasons that you don't change a thing in the measurement system other than turning off the signal. Which is what I did.
Here is the same measurement as above but with the two overlaid:
View attachment 229173
His beef with lack of parameters is non-sequitur. It is Rob's measurements that are so situated. I went out of my way to explain all the relevant parameters in my testing.
Conclusions
This test required using HP mode because that is what Rob used to make the claim of no noise floor modulation and ultra low distortion. Now, if he is saying Rob turned off the HP mode in his noise measurement, then that adds to the problem as Rob should have been very clear that the two measurements were performed differently.
Finally, both DACs were treated the same. It doesn't get more fair and proper than this.