Literary / written register, common in fiction, poetry, and descriptive prose. In conversation, 音乐 ("music") or 音乐声 is more typical. 乐声 specifically frames the music as ambient sound being heard, often from a distance.
mistakes
The character 乐 has two readings: yuè ("music") and lè ("happy"). 乐声 is yuèshēng ("music sound"), NOT lèshēng. Compare 音乐 (yuè reading) vs 快乐 (lè reading).
