I have an older ASUS ROG which uses Realtek for sound. For reasons I am unable to comprehend, it has begun adding sound compression despite this being switched off in all areas where this might be enabled.
Settings
Windows sound settings

I have switched off lower volume in Sound → Communication. (‘When Windows discovers communication activity: Do nothing.’)

All improvements have been switched off via Sound → Speaker → Properties → Improvements. In the same window, sound is currently set to 24-bit 48 kHz; I tried reducing it to 16-bit 44.1 kHz, but it made no difference. Spatial sound is not available.
Device settings
There are no hardware sound issues found, and what currently is installed, is NVidia High Definition Audio (which has never worked), NVidia Virtual Audio Device (Wave Extensible) (WDM) and Realtek High Definition Audio.
The current version for Realtek HDA is 6.0.1.7874 (6 July 2016).
Realtek settings
In my Realtek control panel, nothing is visible at all in the AudioWizard, Sound Effects are set to none and volume leveling is switched off; this applies to both the Speakers tab and the Digital Output tab.

Realtek Sound Effects tab. The Digital Output tab looks the same. The bit sampling rate is the same as in Windows sound settings: 24-bit and 48 kHz.
Playback experience
The volume leveling (sound compression) is especially audible on albums such as Elder’s Reflections of a Floating World, Dimmu Borgir’s In Sorte Diaboli or Frank Klepacki’s live performance at Magfest. All my music is ripped from my personal CDs to FLAC using Exact Audio Copy (except the Magfest show).
I have tried playing back the music both in VLC and Windows Media Player, and it is the same in both. I should further add that sound compression is switched off in VLC. (There is no setting for this in WMP as far as I know.)
Summary
I have had this issue previously, a few years ago. But somehow, probably with a driver update, it just disappeared. I have no idea what is causing it now, and would very much appreciate it if anyone has any method for solving this. And so, to clearly state my question: How do I remove volume leveling (sound compression) in Windows when it is switched off in all relevant settings, both in Windows’ system settings, and in the media players I am using?