This looks great, and is very original.
But I didn't sing at all, and invocation still worked (or so it seems).
Does singing actually change anything?
Viewing post in The Chant of Cthulhu jam comments
I wanted the game to be more about "play" and "performance" rather than "checking your homework" and it being frustrating having to repeat things because you did them "wrong".
So you technically don't need to sing, but singing makes the game more fun, especially hearing yourself harmonizing with yourself, and hearing it build piece by piece.
I could have made that clear in the game but I wanted to try to trick the player into having fun.