User`s guide

'channel number' setting for the oscillator and the last one simply changes
voltage from about 3 volts to about 0.5 (for you EE
folks out there, this is the negative edge of an output-valid strobe).
External hardware is responsible for splitting off the various channels (4 bits
means that there can be 16 of them) and outputting them seperately. The
motherboard hardware just ignores the channel setting and mixes all the sound
outputs into the speaker/earphone. The sound connector on the motherboard only
has room for 3 of the four bits, so expansion cards that plug into the sound
connector can only get 8 seperate output channels. Most stereo cards (AE's sonic
blaster, for example) only pay attention to
the lowest bit, so even numbered channels are left and odd numbered channels are
right (or is it the other way round? I forget).
No, it isn't simple, but it gives a lot of flexibility -- most of which is
largely untapped.
______________________________
From: Keen Jeffrey Alfred
002- Is there a way to output quadrphonic sound on a
IIgs?
We all know that the "S" in GS stands for sound. Stereo cards abound but
the GS is capable of much more. The following circuit uses the same technique
as stereo cards to decode stereo but decodes quadrophonic. Inside the GS by the
memory expansion slot exists the J-25 sound expansion connector that most stereo
cards use. The pin outs are as follows:
J-25 Connector
1 Analog to digital in (end nearest front of computer)
2 Analog ground
3 Waveform out
4 Channel address zero
5 Channel address one
6 Channel address strobe
7 Channel address two
The analog in (pin 1) doesn't concern us here. The waveform out is the
important signal. The contains the output of all oscilators one after the other
in quick succession (the DOC only handles one at a time). When the DOC is
outputing the waveform from an oscilator it puts the channel address from the
DOC register $A0 + osc (most significant four bits) on the three channel address
lines and pulls the channel address strobe low. (The DOC realy has four lines
but only three are connected in the GS).
The circuit below uses the first two lines the decode the channels
(creating 4 unique channels) and breaks the signal into four parts depending on
the address using cmos single position single toggle wired as dual position
single toggle switches. Then the chopped output is smoothed with an active low
pass filter with a corner frequency of 17.7KHz.
Because most programs only use stereo the second channel address in
normally low so this circuit will also decode stereo and this will turn up at