Apple II
Technical Notes
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                                                  Developer Technical Support


Apple IIGS
#19:    Multichannel Output with the Apple IIGS Note Synthesizer

Revised by:    Jim Mensch                                       November 1988
Written by:    John Worthington & Jim Merritt                       June 1987

This Technical Note discusses multichannel sound with the IIGS Note 
Synthesizer.
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It is possible to play multichannel sound using the IIGS Note Synthesizer Tool 
Set.  The Ensoniq Digital Oscillator Chip (DOC) supports 16 independent output 
channels.  Since only the low three bits of the output channel number are 
available through the IIGS sound expansion connector, multichannel circuitry 
may only decode eight output channels (zero through seven).  Output channel 
eight maps onto channel zero, channel nine onto channel one, etc., and this 
mapping continues through all 16 channels.

The setting of the high nibble of the DOCMode byte in a waveform of the 
waveList portion of the instrument definition determines the routing of output 
from a Note Synthesizer instrument to a particular channel (the actual DOCMode 
information is in the low nibble of the DOCMode byte).  You may assign each 
separate element in a waveList to a different output channel to create 
multisampled instruments in which some samples play on the left speaker and 
others on the right.

Apple standards require stereo expansion cards to map all even output channels 
to the right and odd channels to the left.  To be compatible with cards that 
decode more than two of the chip's output channels, software should use 
channel zero for right and channel one for left.  This convention ensures that 
output is always positioned properly in the stereo space with channel zero 
information going to the right front and channel one information going to the 
left front.


Further Reference
o    Apple IIGS Toolbox Reference, Volume 2
o    Apple IIGS Toolbox Reference Update

