Re: [microsound] Theremins with true sine output?

[ndkent <ndkent@xxxxxxxxxxxxx>]

> you could try the theremin CV source made by Doepfer (A-178 THER)
> http://www.doepfer.de
> which outputs just the control voltage, which you could map to yr  
> VCO's.
>
> Aaron Ximm wrote:
>
>
> > I'd like to be able to do this performatively but have been  
> > looking for
> > something more expressive than a signal generator interface (e.g.  
> > a knob
> > for frequency and a knob for amplitude). The gestural interface of a
> > theremin seemed ideal.


For what it's worth the Doepfer the process doesn't involve "mapping"  
- there is no map, that's a term better applied to MIDI data for  
instance, simply put Doepfer makes some Theremin-like antenna modules  
that output control voltages as you've mentioned. You can use that  
voltage to control or be scaled to control anything that accepts  
voltage control. Doepfer makes VCOs with sine waves.  I just paused  
on the word "mapping" because I believe one of the main attractions  
of un-digitally assisted analog technology is a complete lack of maps  
and the inherently stepped/quantitized data involved (nothing wrong  
if you need it but neither sine waves nor theremins are stepped to  
begin with)

Now here's some personal experience. Deopfer basic A-110 VCO sine is  
misshaped enough for me to hear harmonics. I scoped it when I  
suspected and sure enough it has a bump.  Their A-111 VCO  has a  
clean enough sine wave that I can't hear harmonics but is rather  
pricey (made with an IC chip developed for synths back in the late  
1970s). You could save money with a self resonating filter. A voltage  
controlled filter that self resonates tends to produce very pure  
waves. Serge Transform Systems, a maker of fairly high end analog  
modular gear points out that their multimode filter's outputs (each  
with naturally occurring phase shifts) makes for an excellent source  
of low frequency sine waves in quadrature (four 90 degree phase  
offsets between the various outputs).

Serge for what it's worth has a Waveshaper that can shape a saw to a  
sine. I believe they originally marketed it because their earlier and  
less costly VCO did not include sine waves... but the great bonus is  
you can voltage control your waveshape between the two or run other  
waves through as an experiment. Not cheap though.


That's what I think is at the heart of the feature issue (Theremin  
with sine waves). Capability to produce good sine waves with analog  
circuitry isn't lacking, the capability to do it for cheap enough to  
build in a *commercial* Theremin where list price is any concern is.  
That's why you don't see it. It doesn't cost that much but way too  
much to just throw in an accurate implementation as a feature.

If you have a theremin with a control voltage output then you just  
need a suitable VCO with a sine output and probably a VCA to control  
it's output volume from the amplitude antenna. If you need it in one  
unit, someone who does custom analog enclosures could likely  
repackage and power the couple circuits(modules) you'd need. You'd  
then have your Theremin with a true sine output.

nick
http://technopop.info/ndkent/
http://www.technopop.info/panik/dct.jpg
(doepfer theremin setup)



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