[sdiy] Alternatives to Faders

[Tom Wiltshire]

Edward,

On 7 Mar 2007, at 15:08, Edward King wrote:

> you know the pitch-bend and modulation wheels you normally get on 
> synths?
> Thats the way Im going at the moment...although the wheel Im using is 
> okay, Im having problems finding wheels / dials that are similar to 
> modulation wheels so if anyone knows of any, I would be very grateful. 
> They need to be roughly 10mm wide and the same diameter (or close to 
> it) as modulation or pitch-bend wheels.

I don't know of any, but I recently looked into buying 10mm acrylic 
sheet with a view to cutting circles out of it for exactly this 
purpose. I was only going to need two, so thought to do it by hand, but 
if you needed lots, you could probably get someone to machine them for 
you.


> The only issue Ive found is that the level display is inadequate for 
> fine control. Consequently, Ive come up with the following idea:
> for each track, 2 x 3 digit 7 segment displays, one above the other. 
> The upper one should be the level (i.e 0 to 255 or 0 to 100) with the 
> lower one displaying "fine tune" (again 0 to 255 or 0 to 100). Using 
> both 0-255 gives us 16 bit level control and coupled with a rate 
> button, this gives us a reasonable amount of control with enough to 
> response rate to make them practical.

0-255 makes sense to electronic engineers and computer geeks, but 
doesn't make much sense to people who don't count in hexadecimal.

I have also struggled with the problem of how to represent high 
resolution digital values (even 10 or 12 bit is hard) using LEDs or 
such like. One thing that is worth remembering is that analogue 
controls don't really display the position with the theoretical 
infinite resolution they're capable of. Consider: My Korg Polysix has 
scales marked 0-10, with 5mm between tickmarks. Assuming the human eye 
can differentiate positions down to 0.5mm, I could recognise only 100 
different positions on the scale. Even assuming that I could recognise 
positions only 0.05mm apart (highly unlikely) only gives me around 10 
bit resolution.

One solution that I wondered about was to use bicolour LEDs for the 
level display, with one colour representing the coarse value, and the 
other colour representing the fine adjustment. Some rotary encoders 
include switches so that you could push-and-turn for fine adjustment 
(or coarse, whichever way round you prefer). Still, you'd need probably 
32 LEDs per control to get decent resolution this way.

A final problem that your recycled-mouse idea might have avoided is 
that commercial rotary encoders often don't have that many positions 
per rotation - 24 pulses per rotation is a common value, although by no 
means the only one available. This makes doing large changes of high 
resolution controls quite difficult. If the control has a 16 bit 
resolution and one full turn takes you from 0 to max (65536) then each 
of the 24 clicks represents 2730 units. How then to make a parameter 
value jump 2730 units without an abrupt change?

Sorry not to offer more positive suggestions, but this is definitely 
still a problem for which a really good solution is yet to be found.


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