This is the circuit that generates the "score" or "miss" sound. It uses the vertical counter. When a miss happens, it starts a 555 timer that brings its output high for about 242 ms. That output is NANDed with bit 5 of the vertical counter. Since the vertical counter restarts at 262, the result is not a pure square wave; it has a harsher quality to it.

Wait for the Audio Out to fill up, then click "Play Audio".

Next: Hit Sound.