[sdiy] How do contemporary velocity sensitive midi pads work?

Tom Wiltshire tom at electricdruid.net
Thu Aug 6 23:30:21 CEST 2015

Very interesting, thanks! I particularly enjoyed "fingertip vs fingernail". It sounds like you've got lots of potential expression to work with.

On 6 Aug 2015, at 20:44, nvawter <nvawter at media.mit.edu> wrote:

> I've been working with Sensitronics' FSRs for about a year now.
> Electrically, I use a divider circuit with (IIRC) a 3k resistor.  I've found I don't need to buffer
> the electrical signal into the ADC on the STM32F4.  One really should, but really it just makes a
> different curve.  :)  I am open to experimenting with different curves such as with a logarithmic amplifer, etc.,
> if anyone has any suggestions.
> I've been obsessively figuring out different ways to utilize the continuous values to emulate plucked strings, drum
> heads and pressed keys.  My goal is to be able to press lightly with one finger while striking with the other
> and have the tone come out a higher pitch/thinner and decay faster...  sort like muting a drum head or strings
> while striking it.  I've also been trying to emphasize the sound differences between a fingertip strike and
> a fingernail strike!  I know it's possible, I've recorded the electrical signal and identified different
> frequency content.  The challenge now is to transduce it into sound.  There is lots of potential here, guaranteed
> to keep you up late at night for years :)
> One other interesting thing I found with them was feedback when I built a drum with them.  The speaker in the drum
> was able to induce a detectable signal in the FSR.  Not sure if that was vibration or EMI, but it can happen :)
> On 2015-08-05 22:25, Chris McDowell wrote:
>> Howdy list,
>> I'm wondering if anyone has some experience with the design of modern
>> velocity sensitive pads (just found myself curious).
>> Controllers like the akai LPD8 don't appear to have piezos, but do
>> have concentric squares on the pcb underneath each pad. I can kind of
>> guess that these may work like the staggered switches that provide
>> velocity on a synth keybed, but it's not super clear. I've read a bit
>> about "velostat" and FSRs also, and am wondering if they're perhaps
>> doing the deed. I know older MPCs do indeed have piezos, and that
>> seems pretty straightforward. Any info is appreciated!
>> Cheers,
>> Chris
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