SynthModules

> From looking at existing programs, the range of the ADC and 
DAC
> variables look like they range from 0-4095, which appears to 
coorespond
> to the voltage range 0-5 volts.  Is this correct?

The PSIM-1 DAC outputs are scaled for use with the MIDI note 
system and 1 volt per octave analog VCOs simultaneously. MIDI 
notes range from 0 to 127. Now a piano only has 88 keys, not 
128, so some of those notes are "imaginary" in a musical 
sense.

The 12 bit DACs have a 10.666 volt full scale. DAC1V = 4095 will 
send 10.666 volts from the DAC1 output. This means that 32 
DAC steps produce a voltage step of 0.083 millivolts, or 1 
semitone for a 1 volt per octave analog VCO. As scaled, 5.000 
volts from the DAC = Middle C on Piano.

BUT, analog VCOs do not like to be centered around 5 volts from 
the keyboard controller. It puts too much limit on the coarse tune 
control. So we subtract an offset from the MIDI value before we 
send it to the LOADALLDACS subroutine.

Here is a code example. DAC1V is the variable used to transmit 
raw DAC value for channel 1 to the above subroutine.

DAC1V = (MIDINOTE - MIDIOFFSET)*32

If MIDIOFFSET is 36, then middle C is set to 2.000 volts, which 
analog VCOs will like a lot better.