[sdiy] Alternatives to Faders

[Edward King]

Richard,

Comments added inline

Regards

Edward


----- Original Message ----- 
From: "Richard Wentk" <richard at skydancer.com>
To: "Tom Wiltshire" <tom at electricdruid.net>
Cc: "Edward King" <edwardcking2001 at yahoo.co.uk>; "Synth-DIY (list)" 
<synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, March 07, 2007 9:09 PM
Subject: Re: [sdiy] Alternatives to Faders


>
> On 7 Mar 2007, at 17:40, Tom Wiltshire wrote:
>
>> 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.
>
> I think an interesting design would be mod-wheel acrylic with colour- 
> coded LED backlighting, varying with the applied level, or even used  as a 
> rough guide to active channel dynamics - e.g. the colour could  indicate 
> peak or RMS level.

I have this aspect designed in (see a previous post).
Basically, I have LED level display at the side (10 LED's, 5 green then 3 
orange then 2 red)
and numerical values at the top (3 digits for coarse and 3 digits underneath 
for fine)
This - I believe - gives a nice mixture of general level and accuracy.
I think this is a bit different to what you're suggesting, but backlighting 
would complicate things for me beyond what Im trying to achieve.


>
> Four LEDS per wheel -= blue, green, orange/yellow and red - would add 
> hugely to cost and complexity. But it would look extremely cool in 
> action. :-)

It would indeed. I wonder if theres a way to do this under a dark plastic 
panel?

>
>> 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.
>
> Really, you can't. And given that even long-throw faders max out at  maybe 
> 9-bits of precision - 10-bits if you really push the design -  the reality 
> is that any fader or knob control surface has strictly  limited physical 
> resolution.

I suppose that depends on the individual needs of the operator and / or 
where and how the generated values are going to be used. Given that there is 
likely to be several stages of processing between the rotary fader and the 
audio generation system, it doesnt hurt to start out with as much accuracy 
as possible. Moreover, as this a rate thing (rather than an analogue 
position thing), the difference between data width is processor time, not 
hardware cost.
I dont agree with above statement because rate - over position - essentially 
means that the limitations are down to calculations between the slowest you 
can possibly move the rotary fader versus the fastest you can move it. If 
you want really fine accuracy, move the thing very slowly. If you want to 
jump to max or get somewhere quickly, flick the thing or rotate it quickly 
and get ready to hit the "hold" button when you see the level meter getting 
close to where you want to be, moving it slower as you get near there.


>
> Hex appears on MIDI and keyboard controllers often enough not to be a 
> problem in the keyboard market. It's more of an issue in the mixer 
> market, where audio engineers may be less used to it. But there's no  good 
> reason not to map 2 digit hex to a 0-99 decimal display if  that's going 
> to be a problem.

I havent decided yet whether to use 0-255 or 0-100. Ive designed the thing 
with 3 digits each for the coarse and fine values to cater for both.
Hex is only used in the assembly language I wrote for the PIC controller but 
I had no plans to use hex for the actual displays....
I dont know where the idea of hex has come from?


>
> Things like zipper noise and fade smoothing are usually more of a 
> problem. Some digital designs ignore them completely with - as they  say - 
> hilarious consequences.

As this isnt directly connected to audio output, any errors wil be as a 
result of interpolation or the LUT's.

>
> Richard 


		
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