Pitch Memory Training
Highly rated exercise in playing the piano by ear.
Given a single note, can you identify its pitch? Select 'Play Note' and listen. Then try to play the same note back. Once you are happy with your choice, select 'Confirm Choice'.
Challenge yourself to see if you can get ten out of 10. Make sure you get that green light on constant stream. Start with this game, and once you have mastered it, then go on to the more difficult ones, such as Play That Melody and Interval Training.
Make it more challenging by setting a time interval before you play back.
Practice and see whether your average distance gets lower over time.