I play CotN on iOS 10, iPod touch 6th gen
This has been asked for but I never found out why it wasn't implemented in the game. I found that the default beat detection is a little bit earlier than the actual beat of the music. It may be a visual glitch (beat bars that meet at middle) but I found that I got consistent beats without missing by pressing a little earlier. Pressing early on bolt can really mess up with your rhythm cause you to drop a beat. I also play on the computer and calibrating really helped me get through bolt (can flawless death metal low% with calibration). On CotN PE, I can only get to 1-3 average(can get zone 3 or 4 consistently on PC) which is a huge difference.
I think the reason(s) why calibration wasn't put in the game is:
1. All (apple) device should have same imput time unlike keyboards
2. It is not possible to calculate the input and calibrate on a mobile device
3. I'm an idiot and think that the beat detection is off because I'm not noticing that I'm not pressing at the right time
A reply would be nice, it would be better to know that development team is taking a break rather than not knowing anything at all.