I replaced it with a variable Val, and I tried decrementing it infinitely(Val--) in the void loop() function. The pitch changed, but their isnt much of a range at all. It was also strange because even though I was decrementing the value, the pitch only changed if I did a Serial.println(Val) in void loop().
Interrupts are tricky business, I'm beginning reading about them but so far I am totally confused.