Warning: theorizing only post!
Hi Guys,
I recently had a discussion with some musical-instrument guys about pickup systems - specially the piezo type.
It seems that there was (at least some) consensus that the harsh sound you'd most often get from these systems isn't because of the pickups acoustic/mechanic properties themselves, but because of the very-very-large peaks in signal level at the attack of e.g. picking a string, which in turn overloads the preamplifier stage, if this is set to a gain that is anywhere usable for "the rest" of the signal. And this initial overload causes the annoying sonic signature of the piezo systems.
So basically a problem in too-large a dynamic range. And compressing later on doesn't help much, as it tends to clip already in impedance-converter stage.
Which makes me think: Why not make a full-passive fast compressor to act on the signal already before it leaves the instrument?
Couldn't it be done this way:
A simple FET voltage divider, with relatively high series-resistance (in order not to load the signal too much during attenuation) - and a separate "sidechain" piezo device, that directly drives the gate of the FET through a simple passive rectifier-and-capacitor timing. Yes, small capacitor and large resistors, but FET should have no problem with that. Probably some sort of a detector diode needed, germanium?
Should be possible entirely "passive", no battery needed - as the power needed to turn on the FET is easily generated by the second piezo (that can be placed either close to the "audio" pickup, or where the "thump" is louder than what you'd want in your audio).
As this is theory-and-speculation only - my question is: What did I miss, why (if not) hasn't this been done?
Jakob E.
Hi Guys,
I recently had a discussion with some musical-instrument guys about pickup systems - specially the piezo type.
It seems that there was (at least some) consensus that the harsh sound you'd most often get from these systems isn't because of the pickups acoustic/mechanic properties themselves, but because of the very-very-large peaks in signal level at the attack of e.g. picking a string, which in turn overloads the preamplifier stage, if this is set to a gain that is anywhere usable for "the rest" of the signal. And this initial overload causes the annoying sonic signature of the piezo systems.
So basically a problem in too-large a dynamic range. And compressing later on doesn't help much, as it tends to clip already in impedance-converter stage.
Which makes me think: Why not make a full-passive fast compressor to act on the signal already before it leaves the instrument?
Couldn't it be done this way:
A simple FET voltage divider, with relatively high series-resistance (in order not to load the signal too much during attenuation) - and a separate "sidechain" piezo device, that directly drives the gate of the FET through a simple passive rectifier-and-capacitor timing. Yes, small capacitor and large resistors, but FET should have no problem with that. Probably some sort of a detector diode needed, germanium?
Should be possible entirely "passive", no battery needed - as the power needed to turn on the FET is easily generated by the second piezo (that can be placed either close to the "audio" pickup, or where the "thump" is louder than what you'd want in your audio).
As this is theory-and-speculation only - my question is: What did I miss, why (if not) hasn't this been done?
Jakob E.