Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site ut-sally.UUCP
Path: utzoo!linus!philabs!cmcl2!harvard!ut-sally!crandell
From: crandell@ut-sally.UUCP (Jim Crandell)
Newsgroups: net.music.synth
Subject: Re: Synthesizer Controlers:  A New One?
Message-ID: <3386@ut-sally.UUCP>
Date: Wed, 6-Nov-85 14:57:34 EST
Article-I.D.: ut-sally.3386
Posted: Wed Nov  6 14:57:34 1985
Date-Received: Fri, 8-Nov-85 07:35:59 EST
References: <1586@teddy.UUCP>
Reply-To: crandell@sally.UUCP (Jim Crandell)
Distribution: net
Organization: U. Texas CS Dept., Austin, Texas
Lines: 52
Summary: 

In article <1586@teddy.UUCP> mjn@teddy.UUCP writes:
>I've been doing some thinking lately on non-keyboard controllers for
>music synthesis (no doubt a common musing for some of you as well). ...
>Many years ago (1930's ?) there was an instrument developed called the
>theramin.  This device sensed the position of the musician's hands in
>relation to probe sets.  These are usually set at right angles to 
>eachother.  By moving your hands through the air, one could control a
>VCO with one hand and a VCA with the other....
>Now suppose that we take the output of the positions sensors and use
>them directly as control signals to a modern synthesizer.

Interesting idea, although I'd bet it's not new.  Might be fun to play
with.  Personally, I can't get too enthused about the Theremin's
expressive possibilities; I'd recommend that anyone who's seriously
contemplating doing something like this try one before investing
a lot of time and money in such a project.  Of course, I'd be pretty
short-sighted if I failed to admit the possibility that more sophisticated
electronics could really turn the intstrument around.

>One last thought.  The original theramin used some sort of electromagnetic
>field to sense hand position (capacitance? radar?).  A more modern (and
>probably cheaper) construction could involve distance or motion sensors
>similar to the ones marketed by Polaroid.

It would be extremely interesting to find anything so sophisticated in
an electronic instrument of that vintage.  Capacitance to sense hand
position is exactly right.  For pitch control, it consists of a metal
rod (typically) wired to the hot side of the oscillator tank.  A closer
position of the hand increases the capacitance across the coil, lowering
the frequency of the oscillator (this is NOT an audio oscillator,
by the way.  The audio signal is the lower AM product of the oscillator's
output and that of an internal fixed oscillator).  Since the body
conducts RF signals nicely, the other hand serves conveniently
as a plate of a capacitor coupling the signal into an amplifier --
closer position (more capacitance) means more volume (more coupling).

I doubt anyone will find a cheaper way to do exactly the same thing
today.  If you want something cheap and dirty to experiment with, you
might borrow an idea that showed up in Popular Electronics (of all places)
some years ago -- use a pair of CdS or CdSe photo cells (you shade them
varying amounts with your hands.)  Naturally, linear control characteristics
would be very difficult to achieve over reasonable distance ranges, and
besides, everything changes with minor shifts in ambient lighting.
Frankly, I wouldn't expect much of this scheme in a performance setting,
but one might be able to get a feel for what could be done with better
hardware.  Anyway, the photoresistive cells give you analog (resistance)
control signals to work with; what you do with them is your problem (but
then, that's the easy part, right?  [:-)]).
-- 

    Jim Crandell, C. S. Dept., The University of Texas at Austin
               {ihnp4,seismo,ctvax}!ut-sally!crandell