character was at an opera and crying during the performance. I recognized the melody of the song since it seems like the most popular of all opera songs. Although, I couldn't repeat the sound of it now. It is just one of those things where if I hear it, I recognize it. But I have no idea what it would be called or how to find it.

Any ideas on how to find something like that or guesses on what the song might be from my sparse explanation?