[sdiy] scanned pots "jumping"

[cheater cheater]

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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