I remember hearing it’s a pasuk in Shir HaShirim (2:14) ?????? ?? ????? ???????? ?? ???? ?? ???? ??? ?????? ????. This implies that the voice of a female is also a pleasing, attracting beauty of her, not to be shared with a strange male. That is the source. It’s complete application and halachos are discussed in Shulchan Aruch, as any other Jewish laws.
