by ear
She plays the piano by ear.
Mi abuelo es un poco duro de oído.
My grandfather is a little hard of hearing.
Tom toca la armónica de oído.
Tom plays the harmonica by ear.
Tom es muy bueno tocando piano de oído.
Tom is very good at playing piano by ear.
¿Sabe leer música o toca de oído nada más?
Does he know how to read music or does he just play by ear?
No me dijiste que fuera duro de oído.
You didn't tell me I was hard of hearing.
— La Nuit américaine (1973)