By Jay Zimmerman and Jim Nitchals. The choppiness was key: it played the note uninterrupted (literally!) for just long enough to let the listener ascertain the pitch, but not so long that it interfered with the rest of the game loop.
I never disassembled it, either, but my teenage ears sensed that the sound was still playing, albeit at a near-inaudible frequency, even during musical pauses. I assumed the game would set a memory location somewhere to indicate the note to play, and the sound routine's job was simply to play that note (probably attempting to keep a constant time as the frequency varies). That kept the frame rate consistent even if there wasn't sound to play.
I never disassembled it, either, but my teenage ears sensed that the sound was still playing, albeit at a near-inaudible frequency, even during musical pauses. I assumed the game would set a memory location somewhere to indicate the note to play, and the sound routine's job was simply to play that note (probably attempting to keep a constant time as the frequency varies). That kept the frame rate consistent even if there wasn't sound to play.