Ok I see, yeah you are right there are some RNG here (not determined by the seed) you can get a very slow or a super fast wave to sync, but whatever : the back wave speed modulate "randomly" anyway (it would have been too easy without that)
Maybe the sound feedback is not clear enough, maybe I should tweak this part to give more information to the player. I made this puzzle around the following idea :
1 : adjust the Y axis once and for all ( I added red mark on the oscilloscope just after your comment, maybe not the best idea)
2 : Click and drag CONTINUOUSLY the X axis slider to adjust the wave in real time to sync.
3: Profit
Thanks for your feedback, I had no playtesters except me during the developement, it's really hard to make a fair and balance game for everyone and I have to work a lot on that point, cause the game seems very easy to me but I ignore what append on the people minds, how theyre interact with it, anyway there are so much to say about the difficulty balance in video game... : )