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Old 9th May 2013, 10:30 PM   #1
diyAudio Member
Join Date: May 2013
Default Mic as filter

Hello all.

Short and sweet:

I've joined this online establishment to seek information concerning the use of a contact microphone's output as a filter to effect the shape of an instrument input.

Longer and hopefully less confusing:

I want to put the piezo transducer on, let's say, a reverb tank. Then shake the tank a bit so the spring bounces around. I want to use that sound to shape the input signal of an instrument, whether that's vocals, guitar, cornet, etc.

Can anyone wager a helpful guess on how I could go about this?
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Old 9th May 2013, 11:35 PM   #2
Enzo is offline Enzo  United States
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Join Date: Sep 2004
Location: Lansing, Michigan
Why not just use the output signal from the pan that is already there?

The springs bounce around and make noise electrically, but they don;t really make much sound on the pan itself other than the occasional clank. The output transducer puts the spring noise on the jack marked OUTPUT.

From your description it sounds like you want to use a reverb pan that is not in use for something else. As opposed to picking up what it is doing inside while reverberating a guitar. But if you wanted the reverb envelope in a guitar amp to modulate something, you still could draw off the output of the pan either right at the pan or after a buffer stage inside the amp.

The output of a pan will plug directly into an amplifier and can be amplified, after all th reverb return on an amp is just another input to the amp. In fact that is an old trick for something like a Deluxe reverb. The return cable from the pan output jack was umplugged from the reveb jack on the back of the amp, and routed instead to teh commonly unused "Normal" channel input jacks. Now the controls on that channel become th reverb controls, even including the tone controls.
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Old 10th May 2013, 09:22 AM   #3
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Join Date: Aug 2006
Location: W.Sussex
It's that word "shape" that's confusing me. Du you want a vocoder style controlled filter to change the harmonic structure of the vocals or guitar, or a ring modulator which changes pitch, harmonic and volume?

I agree with the previous poster about the reverb spring – it's already set up with an output, just needs plugging in – but contact mics on gongs, thunder sheets, bed springs – why not? All you need for a piezo is a high impedance input (possibly not all that high if the instrument has lots of infrasonic frequencies, but you can always put a resistance in parallel to bring it down, better to start in the multi megs), they produce lots of level.

At this point in history it's probably easier to go for software vocoders or ring modulators, or buy second hand stomp boxes or rack units rather than build your own (as I was forced to, there not being anything of that style on the market). Unless you have your own idea for a hitherto unexplored modulation technique, in which case, best of luck.
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Old 10th May 2013, 07:41 PM   #4
diyAudio Member
Join Date: May 2010
Location: Chicago IL, Long Beach CA, Vienna VA
That's sort of what the transducers on a plate reverb do. There's a driver mounted on a steel plate, and several motion detectors (A piezo ic would suffice).

Unfortunately, mounting them on a Ferrari won't make my guitar sound like a V-12, and mounting them on a Bosendorfer won't make it sound much like a piano, and mounting them on a tenor won't help you sing opera. But on the other hand mounting them on a metal trash can lid will make everything sound somewhat like a trash can lid.
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Old 11th May 2013, 12:38 AM   #5
Enzo is offline Enzo  United States
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Join Date: Sep 2004
Location: Lansing, Michigan
I had assumed the idea was going to be like a Vocoder or maybe a guitar talk-box sort of thing.
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Old 11th May 2013, 09:36 AM   #6
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Join Date: May 2013
I guess what I'm looking for is basically a vocoder, only using a contact mic instead of one that utilizes soundwaves in the air. Chrispenycate has the idea. Maybe my best route would be to purchase a vocoder, though if the circuit would be simple enough I'd prefer it so I can put in exactly what I need for the instrument I'm putting together.
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