[sdiy] scanned pots "jumping"

Thu Feb 4 00:17:06 CET 2010

Hi,

(sorry for top-posting, just being consistent...)

If the subject is digital filtering, then yes, there are many books  
on the subject.

Neil

On 3 Feb 2010, at 19:10, Adam Schabtach wrote:

> 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
>>>>>>>>
>>>>>>>> _______________________________________________
>>>>>>>> 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
>>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>
>>>> _______________________________________________
>>>> 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
>>
>
>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy

--
http://www.njohnson.co.uk