[sdiy] "Synth design questions" or "Learning from Dave Smith"

[Edward King]

Tom,

if you're likely to continue to expand on your system and possibly include 
polyphony and more complex audio engines, I would look at a digital 
interconnect solution with reasonable bandwidth.
Bandwidth gets eaten up pretty quickly for realtime control and if you are 
likely to expand on your system, you'll lose nothing by jumping in sooner 
rather than later...

My protocol specs and designs are pretty much ready for implementation for 
lower speed stuff (still a little work for the higher speed serial). Ive 
called it Simple Time Critical Audio Protocol and its an 8 bit addressable 
packet switch system. Given that its unlikely to be hosted on a system 
needing more than 255 devices, it should be okay for playing around with.

Is there room on your devices for drivers etc?

EK

----- Original Message ----- 
From: "Tom Wiltshire" <tom at electricdruid.net>
To: "synth-Diy diy" <synth-diy at dropmix.xs4all.nl>
Sent: Thursday, October 18, 2007 1:28 AM
Subject: [sdiy] "Synth design questions" or "Learning from Dave Smith"


> Hi all,
>
> I've been looking at the very interesting guts-out photos of the new  DSI 
> Prophet 08:
>
> http://prophet5.org/prophet08/
>
> I'm always very interested in this kind of thing since it allows me  to 
> see a little of how other people have tried to solve design  problems that 
> I'm looking at myself as part of my monosynth project.
>
> Before I mention that, I'd just like to point out the RJ11  programming 
> connectors for each of the processors on the voice board/ main board - 
> custom firmware for your DSI Prophet, anyone? The mind  boggles!
>
> Ok, now my questions:
>
> 1) Should the main control processor talk to the voice board  digitally or 
> using control voltages?
>
> Originally, I thought I'd use control voltages, since it's simple and 
> keeps the analogue spirit of the voices. I had this in mind when I  did my 
> PIC-based LFO and ADSR designs.
> However, it does seem a little bit daft to have one processor take 
> digital information (patches from memory) and use an D/A to convert  it to 
> a control voltage, just so that another processor (say, a PIC- based 
> envelope generator) can use a A/D to convert it back to a  digital 
> parameter. Consequently, I'm currently wondering about using  a SPI 
> connection instead.
>
> 2) Should the front panel of a programmable synth use pots or rotary 
> encoders?
>
> Again, originally I'd thought pots. This works reasonably well whilst  you 
> have a individual pot for each parameter, although even this is a  bit of 
> a pain with a programmable synth, since as soon as you change  program, 
> none of the knobs tell you anything. When programming my  Korg Polysix, I 
> always have the 'manual' button pressed, so that the  sound I hear is the 
> one I can see on the panel. And that's a simple  instrument.
> However, it would be nice to have multiple LFOs or envelopes that  share 
> controls, since this gives much more flexibility without making  the panel 
> enormous . The Prophet 08 is an example of what I have in  mind - its four 
> LFOs share the same group of controls, with simple  buttons to select 
> which one to edit. The trouble with this is that as  soon as you switch to 
> the next LFO, the knobs don't tell you anything  again. Given that they 
> don't, are rotary encoders easier to work with  since you can just pick up 
> the value from where you are without  having to worry about the end of the 
> track? As a technical issue, how  does one go about monitoring 64 rotary 
> encoders?
> So far, I feel the only really convincing solution to this is  encoders 
> with LED rings like Clavia use, but resolution is a problem,  so you still 
> need a LCD to see the true value, although the lights  might give a nice 
> guide. Also, building a serious synth panel with as  many knobs as the 
> Prophet 08 has would require some serious number of  LEDs, and similarly 
> serious amount of current to light them all.
>
> At one point, I'd made decisions about many of these things, but as I 
> learn more, I keep finding more sophisticated ways to do things, and  then 
> wonder if the earlier decision was really so wise in the light  of the new 
> information. I guess I should just get on and build the  simpler 
> instrument I designed originally and save the clever stuff  for the Mk2.
>
> Thanks!
>
> Tom
>
>
>
>
>
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