As someone who hasn't had a piano lesson in about 40 years, I find myself wanting to play with the keys to match the melody. So I hear the initial melody, and then I'm practically hitting keys at random (guessing where I should be on the keyboard) until I find the first note, and then I have to listen over and over again while trying to find the second note. I kind of want to hunt and peck until I'm ready and then get tested to see if I nailed it.
Maybe the answer really is just as simple as a little visual toggle that puts you in a "sandbox" mode where all the sounds still go through, but the game doesn’t respond to them until you untoggle it.
This creates a problem in that it's easy to muddle your way through without learning anything. To prevent this:
Once it gets to the end of the round in this mode, if the user had even 1 wrong note selected in this round, the game will then expect them to play it perfectly once again (like it does now).
This way you get both the hunt and peck exploration and the final "now that you've had your time to get your ears and fingers in order, play it correctly."
Tried safari and Firefox focus