I remember somebody saying "I can hit the high notes" in singing competition, then I'm curious if "key" here is same as "note".

Native speaker’s answer
Rebecca
Here, "keys" refers to a part of the instrument itself, the white and black keys on the piano. However! If you're talking about the sound of keys on a piano, then you could use "note" as well. That being said, usually a "key," in terms of sound, determines what "notes" one plays. Ex: That note was too high to sing, can we try another key? Ex: There's a couple of keys on the piano that aren't working.