South Indian movies are famous for their background scores (e.g., music by Anirudh or DSP). On 9xmovies, the audio is often re-encoded to a low bitrate (128kbps or even 96kbps). This destroys the bass, flattens the dynamics, and introduces hissing sounds. You are not experiencing the movie as the director intended.
: The highest available quality, often compressed into smaller file sizes (HEVC/x265) for easier downloading. 9xmovies+in+south+high+quality
The "High Quality" tag usually refers to several specific rip types found on the site: South Indian movies are famous for their background