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

[Tom Wiltshire]

Jure,

I also think this is a good idea. It's pretty close to the Oberheim  
Matrix12/Matrix 6 interface.

Combined with some buttons to quickly select different groups of  
parameters (VCO1, VCO2, Filter, Filter Envelope, etc etc) and maybe a  
block diagram to give you some sense of the synth's layout, this  
could be really good.

One possible problem is the resolution of a typical rotary encoder.  
These often have 24 pulses per rotation. This means either that you  
need some way of incrementing faster (various speeds) or you have to  
sit there twiddling for ages to reach the maximum value.

I did some experiments trying to control a parameter value with a  
rotary encoder using the rotation speed to control the increment  
size. This sounds plausible at first: you turn quicker, it goes up  
more, you turn slower, it slows down, you turn really slowly, it  
steps up one at a time. I tried both linear and various non-linear  
relationships between rotation speed and increment size.  
Unfortunately I found that I couldn't control it at all. A single  
twisting movement starts off from rest (e.g. really really slow) and  
then speeds up to some maximum value, before slowing down to rest  
again. This makes it hard to get a 'feel' for how much or how fast  
you need to turn for a given result. When I changed it to two or  
three bands (e.g. single-step, fast, faster or just single-step and  
fast) I did better, since I learned to turn at the right speed to get  
the effect I wanted. Still, I wasn't everso impressed. A simple pot  
is much easier to get to where you want it accurately. Perhaps with  
cleverer software than I managed to write rotary encoders might be as  
good, but I couldn't find a way.

Regards,
Tom


On 18 Oct 2007, at 10:48, jure zitnik wrote:

> i've also been thinking about the pots/encoders question recently. i
> kinda figured out quite a cool interface using 8 endless pots (what
> alesis ion uses if i remember correctly) or even rotary encoders PLUS
> a 2x40 LCD display. multiply that as many times you want.
>
> it would look like this - there are two rows of 4 pots/encoders, one
> above the lcd and one below. the display has 2 rows of 40 characters
> each, which means 10 characters of text/numerical representation of
> the parameter that the pot/encoder controls. i hope you can imagine...
> for instance, you could have (should be viewed with monospace font,
> just copy it into a notepad on windows):
>
>     O         O         O         O
>
> VCO1 tune VCO1 fine VCO1 pw   VCO1 morph
> ENV1 att. ENV1 dec. ENV1 sus. ENV1 rel.
>
>     O         O         O         O
>
>
> when each of the pots/encoders move, the display shows value instead
> of name of its parameter. you don't need to see the name of the
> parameter while you're tweaking it. there could also be a dedicated
> 'disp' key near the lcd, that would toggle the idle display mode, or
> it could be just a momentary switch to show the parameters' values
> instead of names. or you could simply use the inverted character
> (light on dark instead of dark on light) mode to graphically represent
> parameter's (approximate, 0-10) value and still show the name at the
> same time.
>
> this way, you can stack a few of such combos on a synth, two of them
> would also make a nice sequencer interface...
>
> what do you guys think?
>
>
> On 10/18/07, Edward King <edwardcking2001 at yahoo.co.uk> wrote:
>> 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
>>>
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> Synth-diy mailing list
>>> Synth-diy at dropmix.xs4all.nl
>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>>
>>
>>
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at dropmix.xs4all.nl
>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>
>