Frequency measurements with different inputs

[krass]

New measurement, from a Macbook Air working on batteries, with Wifi Air. Totally galvanically isolated from the Devialet.



Basically, same problem with a different computer. Checked too sampling rate, etc.

i think it's a comb-filter:
http://www.sengpielaudio.com/calculator-combfilter.htm
according to his diagrams, you are seeing a comb filter effect with a first notch at about 1100hz, first peak at 2.2khz. The other notches are consistent.
I'm not an expert, but he talks about disruptive room reflections with delays between 2-15ms. With your first notch at 1100hz, it looks like you have a disruptive delay of about 0.5ms (which is outside the 2-15 but Im getting a strong feeling of "disruptive reflections" here....).

So I would ask:
do you have well-damped walls ?
is your microphone placement sensible, or is it possibly at a room node, or halfway between 2 reflective walls, or (etc etc).

Why don't you try putting the mic somewhere entirely different, and put some temporary damping around the place just to see.....

I can't prove it, but I'm now 99% convinced it's a test placement/ setup issue.......

(or I'm completely wrong).