by ear
Ele sabia tocar violão de ouvido, sem partitura.
He knew how to play the guitar by ear, without sheet music.
Eu estou com uma infecção de ouvido.
I have an ear infection.
She plays the piano by ear.
Tom toca piano de ouvido.
Tom plays the piano by ear.
I have an earache.
Tom está com dor de ouvido.
Tom has an earache.