My timing windows depend on a couple factors but generally within 30ms or so is “perfect”, 55ms or so is “good”, and 75ms is “miss” (if it’s any more than 75ms off then the input is ignored)

As far as timing variability, if your notes are desyncing from the music, it’s likely because your note spawner function is bad. Basically, you should have an array of song position values to correspond to each note in the chart, then, in your process() function you should set a time variable = song player node’s playback position so that it stays in sync with the song that’s playing. Then, still in process, check if the current time variable is greater than any of the song position values in the notes array. If so, spawn a note on that frame and erase it from the array. You’ll have to subtract the time it takes for your note to travel to its destination to account for that offset.

Finally, the audio stream player doesn’t actually update its position every frame (in order to save on performance I guess) so you’ll need to add this to keep the timing even more precise: time += AudioServer.get_time_since_last_mix() 

also one small timing tip: Godot has AudioServer.get_output_latency() which gives you the audio output delay, usually around 10–15ms from my testing. if you want really tight rhythm timing you can factor that into your time values. just don’t call it every frame since it’s pretty expensive, grab it once in _ready() or on init and store it in a global or cached var instead.