[sdiy] scanned pots "jumping"

Adam Schabtach lists at studionebula.com
Wed Feb 3 20:10:17 CET 2010 

Care to cite some specific references to a few of these "hundreds" of books
on the subject? Since everyone else on this list seems to be so grossly
ignorant about this topic, I'm sure we could all benefit by being given a
couple of specific examples of the sources of your extensive knowledge.
Thanks in advance.

--Adam

> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl 
> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of 
> cheater cheater
> Sent: Wednesday, February 03, 2010 8:20 AM
> To: Tom Wiltshire
> Cc: synth diy
> Subject: Re: [sdiy] scanned pots "jumping"
> 
> Tom,
> it's not complicated because we're not inventing core fusion 
> here (and even core fusion is not that complicated anymore, 
> since it has been invented already). This parameter smoothing 
> is an industry standard that is being used in thousands, no, 
> millions of electronic equipment models being churned out by 
> china every second. It is really not that complex to open a 
> book, one of hundreds on the subject, and copy the listing 
> from there. This sort of knowledge was widely available for 
> about half a century. There is absolutely no thought process, 
> no creative process, and no inventive process involved in 
> implementing this feature, you just have to be awake enough 
> to be able to rip off someone else's widely available code.
> 
> There is no explanation for a manufacturer not to have this 
> implemented except for stupidity/lack of professionalism, and 
> if what is being described is really the case, then I am 
> disappointed with Clavia/Nord.
> 
> D.
> 
> On Wed, Feb 3, 2010 at 16:09, Tom Wiltshire 
> <tom at electricdruid.net> wrote:
> > The simplest way I know of doing this is a running average of x 
> > values. If x is a power of two, the division that is implied by an 
> > average becomes a simple bitshift.
> > This makes a fairly basic LPF, but it works well enough for this 
> > application. More sophisticated filters would probably demand more 
> > processing (FIR typically) or more accuracy (IIR typically).
> >
> > Even with the LPF (or especially without it) it is usual to 
> set limits 
> > either side of the current knob position that the knob must 
> move past 
> > in order for its value to be updated. A LPF will slow down 
> the rate of 
> > ADC jitter, but won't remove it entirely -  for example, any slow 
> > drift due to temp change will get past the LPF.
> > On a 10-bit value, I've found that having limits of current_value-4 
> > and
> > current_value+4 is usually enough, but it'd depend on how noisy the 
> > environment is and hence how much ADC jitter you're seeing.
> >
> > I disagree with D on one point - I think there's a fair bit 
> going on 
> > here, and it is easy to do badly and hard to do well. 
> That's not very 
> > simple. He's right that it's a must, though - you need to 
> deal with these issues somehow.
> >
> > T.
> >
> >
> > On 3 Feb 2010, at 14:40, cheater cheater wrote:
> >
> >> Dave,
> >> no, it is very simple and an absolute must.
> >>
> >> D.
> >>
> >> On Wed, Feb 3, 2010 at 15:35, Dave Kendall 
> <davekendall at ntlworld.com>
> >> wrote:
> >>>
> >>> Thanks.
> >>>
> >>> I could have written that a bit clearer I guess. I leave 
> the pots at 
> >>> certain settings to prevent them jumping. The actual 
> knobs are fine 
> >>> - they don't move, only the parameters jump.
> >>> Interesting that it's a known technique to apply a LPF to the 
> >>> scanning - the sounds and general build quality are good, I was 
> >>> surprised that to see the jumping behaviour. Come to think of it, 
> >>> I've twice had to disassemble it because a key stopped 
> working. In 
> >>> each case a bit of crud had got under the plastic 
> membrane housing 
> >>> the 2 key contacts for each key - this was enough to kill 
> that key. 
> >>> Removing it fixed the problem. I guess that's a 
> mechanical issue - 
> >>> the membrane is not entirely flush with the pcb - it has 
> some small 
> >>> holes where I guess the dust got in.
> >>>
> >>> Shame that the software issue is there - is that sort of 
> thing hard 
> >>> to implement?
> >>>
> >>> cheers,
> >>> Dave
> >>>
> >>> On Feb 3, 2010, at 14:18, cheater cheater wrote:
> >>>
> >>>> Dave,
> >>>> parallax mode is a way of processing the position of the 
> knob. It 
> >>>> requires the potentiometer to be scanned too.
> >>>>
> >>>> If the knobs jump around without you touching the synth at all, 
> >>>> then the knobs are most probably jumping because they 
> have no lag 
> >>>> processor/low pass filter applied to them. If the knobs 
> jump around 
> >>>> when you hit the keyboard hard, then it's a mechanical 
> issue that 
> >>>> cannot be addressed in software.
> >>>>
> >>>> Either way this is not something that should be 
> happening except in 
> >>>> the cheapest equipment.
> >>>>
> >>>> D.
> >>>>
> >>>> On Wed, Feb 3, 2010 at 15:04, Dave Kendall 
> >>>> <davekendall at ntlworld.com>
> >>>> wrote:
> >>>>>
> >>>>> Hi all.
> >>>>>
> >>>>>
> >>>>> Following on from the pots/vs. encoders thing, when 
> playing a Nord 
> >>>>> Electro (with scanned pots, not in parallax mode) 
> occasionally a 
> >>>>> parameter setting will jump, presuambly from the 
> vibration of the 
> >>>>> instrument being played hard. I've got used to leaving 
> the knobs 
> >>>>> in a "safe' position before a gig in case something drastic 
> >>>>> happens, which on occasion it has..
> >>>>>
> >>>>> Is this a common fault with such systems? FWIW, the machine did 
> >>>>> this more often when it was brand new...
> >>>>>
> >>>>> cheers,
> >>>>> Dave
> >>>>>
> >>>>> On Feb 3, 2010, at 00:35, Dave Manley wrote:
> >>>>>
> >>>>>> When an encoder becomes unreliable is it because
> >>>>>>
> >>>>>> 1. the switches are worn out
> >>>>>> 2. the switches are contaminated and need cleaning 3. the 
> >>>>>> mechanical cam that operates the switches is worn out 
> 4. debris 
> >>>>>> from wear on the cam/switches is blocking the switch 
> operation 5. 
> >>>>>> ???
> >>>>>> 6. any and/or all of the above?
> >>>>>>
> >>>>>> Anybody take one of these apart and do an analysis?  Does 
> >>>>>> spraying cleaner into an encoder really do anything?
> >>>>>>
> >>>>>> -Dave
> >>>>>>
> >>>>>> _______________________________________________
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> >>>>>>
> >>>>>
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> >>>
> >>>
> >>
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