see Sound
Registers
Stella
These addresses write data into the audio volume registers which set the pull down impedance driving the audio output pads. D3 D2 D1 D0 Audio Output Pull down current 0 0 0 0 No output current 0 0 0 1 lowest 0 0 1 0 ... ... ... ... 1 1 1 0 1 1 1 1 highest