Frequency measurements with different inputs

[Divasson]

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.......
..... and credit to f1eng who suggested the same thing earlier

(or I'm completely wrong).

---

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).

This is what I thought from the beginning; but it should happen too with the Toslink input (remember that all measures have been made without any change to loudspeakers, room or connections. So Toslink should give the same comb filter effect!

The tests made on Monday of this week were done with the loudspeakers moved around 15cm back each, to avoid these problems. Still the comb filter appears - except on Toslink. Same frequencies.