Boom 3D - Audio enhancer with 3D surround sound
Letasoft Sound Booster - Boosts sound volume above maximum level
Equalizer APO - A system-wide equalizer for Windows 7 / 8 / 8.1 / 10 with channel remapping/copying capabilities
FxSound - Clearer Sound for Your PC. The new FxSound boosts your sound quality, volume, clarity and bass.
eqMac 2 - The open-source macOS audio optimizer 🎛️
Fidelizer - Feel the "Real Sound" with pure audio fidelity