@ShiZo did you disable 'De-Emphasis' (or set it to 'auto')?
This is what it does if enabled:
Source (dead): https://www.rme-audio.de/images/techinfo/emphasis.gif
Source: http://www.sengpielaudio.com/calculator-timeconstant.htm
According to the manual for the ADI-2 Pro FS on p. 72:
This is what it does if enabled:
Source (dead): https://www.rme-audio.de/images/techinfo/emphasis.gif
Source: http://www.sengpielaudio.com/calculator-timeconstant.htm
According to the manual for the ADI-2 Pro FS on p. 72:
The ADI-2 Pro can also perform both pre- and de-emphasis outside the DAC with just a single band of its Parametric EQ. The emphasis filter is based on a simple first order RC filter with time constants of 50 μs and 15 μs. The frequency response curve looks like a low-Q treble boost with its +3 dB point at 3183 Hz, and the upper shelving point at 10610 Hz. At 20 kHz gain hits +9.49 dB.
For an inverted filter curve select band 5 with type shelf active, set Q to 0.5, Frequency to 5.2 kHz and Gain to -9.5 dB. Similarly, a pre-emphasis is done with the same settings but Gain to +9.5 dB.