JP8 quantisation

[WeAreAs1 at aol.com]

On 4/25/99, p_nugteren_van at hotmail.com wrote:

<<I don't remember who said it but which revision of the jupiter8 had 
and 14bit adc/dac? Also could someone point out some differences in 
the revisions of the JP8 (DCB etc.)?
Maybe the simplest solution would be to just put new adc/dac 
convertors into an poly analogue synth, and change the rom. >>

The JP8's with the higher resolution DACs do not have higher resolution for 
the panel controls, or on any voice parameters.  They simply have better 
tuning resolution when using the Autotune function.  The voice parameters are 
still limited to a maximum of 7 bits (although, some parameters have less 
than 7 bits).

Likewise, the Jupiter 6 has a maximum of 7 bit resolution on voice 
parameters, with most parameters using less than 7 bits.  The 14 bit DAC is 
simply there to give better resolution on software-generated pitch controls 
(Autotune, pitch envelopes, LFO's, etc.).  The panel controls, however, are 
still limited to a maximum of 128 steps.

Most MIDI-controlled synths limit their parameter ranges to 7 bits (to match 
the single-byte MIDI value range).  Some synths map certain parameters across 
two bytes, in order to give increased resolution or increased parametric 
range.  This is pretty rare, though.  Most MIDI instruments don't even take 
advantage of MIDI's full 14-bit Pitch Bend resolution, since manufacturers 
have found that most people are reasonably satisfied with 7-bit pitch bend 
(at least when the pitch bend range is set to +/-2 semitones).

<< I'm really wondering how much effort 
and time it will take to reroute the panel CVs to the CVins of the 
circuitry and still be able to switch between the adc and direct CV. 
Or at least change the adc to 16bits.  >>

Changing the resolution would be possible, but not without an Herculean 
effort (and an Einstienian cerebellum, not to mention an 
Admiral-Richard-Byrd-like thirst for adventure and danger).  If you simply 
want smoother real-time parameter control, then the direct CV approach is 
best.  There are really only a few parameters that would greatly benefit from 
smoother CV control.  It could be done with just a few pots.  You would have 
to be willing to have them act as relative offset controls, though.  It just 
wouldn't be practical to have them act as absolute-value replacements for the 
programmed panel controls.  I would use bi-polar pots with a center-detent, 
so you could easily find the "zero" point that would add no offset to the 
programmed value.

This sort of thing would be easiest to do on your JUNO 60, considerably more 
difficult on a JP-8 (depending on which parameters you wanted to access).  
The JP-6 has many software-generated modulation parameters, so it would not 
be possible to put any of those parameters under direct CV control (for 
example, any Envelope Depths or any LFO Depths).  You could still have direct 
CV control over filter cutoff, though (which, I suspect, is what you are 
mostly concerned with).

Michael Bacich