Sound Physics is a mod that overhauls Minecraft's sound engine to simulate reverberation, sound occlusion/absorption, and physically based sound attenuation. The sound simulation provides interesting aural cues; you'll be able to tell whether a mob can be directly seen and whether it's just around the corner or in a closed-off area with your eyes closed. Exploring caves is much more immersive, and reverberation provides a sense of scale to grand structures or large underground ravines.
Shame cause I have resource packs that replace C418's beloved records with music playlists, album covers and all. But hey, a mono conversion would be worth it. Not many think of things like this. Keep up the good work Cody!