Replying to This shit should be in garageband

you know how you can choose an instrument and play it with the keyboard as a piano? why couldnt there be a thing where you hum or sing or whistle a tune you want, then convert it into any given instrument playing those same notes?

cause i always think of sick ass tunes but i can only sing or whistle them, i suck balls at real instruments cause ive almost never played them so it's not like i can think of a song and play it or transcribe it