Question: Is it also a form of singing to hear the song in your mind?

Sri Chinmoy: Certainly. But when you sing outwardly, it convinces the outer mind. If you sing outwardly, you feel that there is a witness. If you don't complete the song, you will be embarrassed. But if you sing in silence, then in the middle of a line you may stop and nobody will criticise you. But when you do it outwardly, at that time you will be exposed. At that time, you feel that the ear is the witness.