I did. There wasn't any impact on distortion of the sine wave. I tested values of 50, 85 and 100.
Apparently the distortion is caused before volume mixer (i have been told), that is why pre-amp -0.14db gain in EQ APO works, but volume mixer in windows does not.
The explanation that there is CAudioLimiter fits, because when I opened Oscilloscope in the software, sine wave wasn't rising beyond -0.14db - eg. some sw imposed limit was distorting it right before my eyes.
I tested external DAC in my NAD d3020 v2 over Toslink.
AUX input had similar threshold at -3.73db. (roughly -4.0db)
Used output was headphone jack on the amp for both measurements.
My wild guess is that Realtek ALC1220 uses some sort of signal boost (enhancement APO) for its analog outputs, but not for Toslink which is affected only by OS.
It was measured over Realtek ALC1220 Line In, Non exclusive mode, 44.1Khz, 16bit, stereo, because I was trying to test sound format used in PC games.
Software is called Audio Tester V3.0. Shareware and terrible
, and I used it only for confirmation of the advices I got.
Edit some other screens:
This is 1Khz sine wave at -0,14db. I adjusted volume on the amplifier to fit the lines, to make it more visible.
View attachment 134064
This is 1KHz sine at -7,7dB. As you can clearly see its smaller, and that is correct.
View attachment 134065
And this is 1KHz at +10db, and its of same size as the first one. That is definitely NOT correct, and it counts as distortion.
View attachment 134066