[sdiy] Percussion MIDI controller

[Magnus Danielson]

From: Ingo Debus <debus at cityweb.de>
Subject: [sdiy] Percussion MIDI controller
Date: Thu, 24 Feb 2005 17:31:36 +0100
Message-ID: <8D5A0D99-8681-11D9-AFBB-000A9571C136 at cityweb.de>

> Hi all,
> 
> Someone asked me about a pecussion MIDI controller like this: a 1...1.5 
> metres (4 or 5 feet) long rod to be played with sticks/mallets. It 
> should sense both the impact and the position where the stick hit it.
> 
> My first idea was attaching two piezos to the rod, one at each end, and 
> sensing the time difference. So I did this and watched the outputs of 
> the piezos on a dual trace scope. With wooden rod and sticks, the slope 
> is way longer than the time difference itself (the speed of sound in 
> solid materials is much higher than in air), and couldn't be seen on 
> the scpoe at all. It's probably difficult to measure the time 
> difference precisely.

I've done exactly this exercise and we had no problem what so ever. We used a
standard Tektronix desktop scope in single-trigger position. We had a 450 us
time difference between the two cases. Converting this time difference into
CV and Gate should be trivial, infact I intend to do the exercise very soon
anyway. We used two piezo-elements and a standard electric PVC tube. Hitting
with a stiff enought object and distinct hit generated enought amplitude for us
not to worry, maybe only impedance buffering, but even that may be unnecessary.

> Then I tried a steel rod and hit it with another piece of steel. Now 
> the time difference became visible, because of the much steeper slopes. 
> But hitting steel with steel makes a lot of noise in itself, so this is 
> probably not very well suited for something controlling a synth.
> 
> Another idea is attaching a resistive wire to the rod and hitting it 
> with an electrically conductive stick, thus sensing the position. This 
> would of course require a cable at the stick. Impact would still be 
> sensed with a piezo.
> 
> Anybody already done things like this?
> Any other ideas?

I will persue down the piezo-element road soon enought. I'll let you know, but
I don't expect by electroncis to be very big and incomprihensible at all.

Duo-phonic may be a bit of a challenge thought... ;O)

Cheers,
Magnus