[LAD] Half-OT: Fader mapping - was - Ardour MIDI tracer

Fons Adriaensen fons at linuxaudio.org
Mon Aug 25 09:18:06 UTC 2014

On Mon, Aug 25, 2014 at 09:47:31AM +0100, Will Godfrey wrote:

> On Mon, 25 Aug 2014 08:13:28 +0000
> Fons Adriaensen <fons at linuxaudio.org> wrote:
> > ... or a charge amplifier.
> Interesting you mention that. I was wondering if that sort of thing would
> work, although I didn't know the name - I had to look it up :)

The output produced by a piezo is an electric charge proportional
to the mechanical input, so a charge amp is the right way to 
capture it, and the standard one for scientific or technical use.

Basically what a charge amp does is to short-circuit the piezo
and integrate the resulting current. And since current * time =
charge, this produces the right output.

What happens with a high-Z input instead is that the capacitance
of the piezo itself plus that of the cable acts as the integrator.



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