Based on your feedback, I have updated the game to provide some help for both predicting the waves motion and give a visual cue for the player. I have added two black lines on each side to help the player know when to press. I've also made the wave particles change based on its state, Green for slow speed, Blue for when it is about to change speeds soon, and Red for fast speed. Looking out for blue will allow the player to predict when the speeds will switch.