by ear
He played the piano 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 es muy bueno tocando piano de oído.
Tom is very good at playing piano by ear.
No me dijiste que fuera duro de oído.
You didn't tell me I was hard of hearing.
— La noche americana (1973)
Tom puede tocar el piano de oído bastante bien.
Tom can play the piano by ear quite well.
Tom toca la armónica de oído.
Tom plays the harmonica by ear.