Fantastic looking game! I like the idea of sending out the arrows instead of reacting to them.
One thing I noticed was that there wasn't necessarily a narrow window that I needed to send a specific note. After getting down the controls and learning to type to the beat, I found that you can press all arrows at once to sort of clear out everything (with the exception of the middle column)
Speaking of, I really like the added complexity of the middle column. Having to decide when to send that one out was really neat. I think adding more of a limitation of how often you can send them out may help to make the game more difficult.
Overall, really cool! Great job c: