REW measurements and 0dbfs level

[snowbl1nd]

Hello everyone,
I’m trying to measure the TempoTec Sonata HD Pro in REW as an example, as I would like to measure some other equipment in the future.
System: RPi4, Raspberry Pi OS (Bullseye), REW (Java), EMU 0404 USB.
The output level is set to maximum, 1kHz tone 0dbfs.
The input level is -6 dbfs according to the technical characteristics, but the REW shows -5.6 dbfs.

Looks good, I think)

At -3dbfs input everything is fine too. Sorry, I didn't take a screenshot.

At -1dbfs the third harmonic part increases,

so at a level between -0.5 and up to -1dbfs the second and third harmonics begin to "jump". Thus it is impossible to make relatively accurate measurements.

Approaching 0 dBFS worsens the performance, and 0 dBFS shows only distortion and a huge increase in noise.

I see that others rarely measure at 0dbfs, but I would like to understand the logic of this behavior.

Thanks!

P.S.
Recording through Audacity gives the same results.

And sorry for re-posting, because Newbie-forum doesn't seem as "responsive", but I don't want to blame anyone)

 

[DVDdoug]

0dBFS is a digital level and there's no automatic calibration with analog levels. If you're doing what I think you're doing the dBFS level will change when you adjust the knobs on the EMU interface.

 

[Sokel]

0dBFS is a digital level and there's no automatic calibration with analog levels. If you're doing what I think you're doing the dBFS level will change when you adjust the knobs on the EMU interface.

Yep.
On top of that,Emu's sweet spot is at about 1-1.5V on it's inputs,it needs a voltage divider to get nice measurements for more.
There are some nice schemes in diyaudio,for making it usable.