This is because every android device plays audio with a slight delay and you need the music to be in sync with the arrows.
You can calibrate right after you hit play the first time or go to Settings/Set Delay
Proper calibration procedure:
- Try to do a loud tap to the screen (with a nail) so you can hear both - the drum sound and your finger tap. This will help you determine if your finger is taping on time with the drum sound and make adjustments
- If you play on headphones, use them also during the delay calibration - the delay can be different for speaker and headphones
- Your delay number turning green indicates that last two taps were within 0.02s accurate and therefore your delay should be set properly. Just press back or continue to finish the calibration
- Find a quiet place so you can hear the drum sound better
- Retry - test your delay and try again
- You can modify the value manually by taping on the delay number
- Fine tune your delay - you can enable in-game tap offset display in Settings/Advanced "Timing Info: SHOW" and fine tune your delay number manually
If you have trouble with music sync (like different sync for some songs) - please check the ?Help/FAQ/Known issues article as you might find some useful info there.