Michael J. Mahon wrote:
No, each reference complements the state of the speaker toggle, with the initial state undefined. So each reference causes the level to switch from 0 to 255 or from 255 to 0, depending on its current level. (The initial state may, in fact, be defined. But after loading ProDOS <click> and getting a few "beeps", it's anyone's guess what the state is--unless all speaker sounds use an *even* number of transitions!)
I think most do use an even number of transitions, since a real Apple speaker will sound markedly different when you start in the "wrong" state. A case in point is the "Ultima V" intro sequence. On the screen with the big "Ultima" title at the top, wait for the third demo scene "The Arrival". Listen to the water's trickling sound. After a while, one of the Shadowlord figures will fire an arrow; the firing sound must contain an odd number of speaker transitions, since after that, the water trickling sounds markedly different. If you keep waiting and let that scene pass by another time, the water sound will revert back to its first version after the arrow is fired again.
Or just try a single PRINT PEEK(49200) before booting a game. Chances are that it will sound markedly different.
Note: this requires real Apple hardware. On most emulators there's no audible difference.
-- Linards Ticmanis