[linux-audio-dev] Theremin-style controller (residual "PdDSP?")

Mr.Freeze theremin at free.fr
Thu Apr 8 23:04:04 UTC 2004

If a PureData-powered expander turns to be a miniITX PC, then I'll stick to the
benefits of my Shuttle barebone!
Let's leave this "PdDSP?" thread have a little rest...

Paul Winkler wrote:
> IIRC, there was a midi theremin-style controller kit available from PAiA.

Not right out of the box actually! The CV outs of the PAiA Theremax have to be
routed to their MIDI Brain in Fader configuration (other other equivalent-in-use
MIDI trigger), so that it sends well-chosen MIDI CC's, but the MIDI Note
On/Off's have still to be monitored by the next-in-chain device.
But check the whole schematic (by downloading the PAiA
"every-month-it's-this-month's" freebie, i.e. the Theremax manual)...
Hard-dying maze!

> Check google, what you want might already exist.

When it comes to renew the Theremin sensing principle, as opposed to remember
the byegone days (no offence here), I think I can slim-out the schematic like
Toby Paddock did here:

QProx QT300/301 are cheap Capacitance to Analog Converter IC's with 16 bit
continuous or 8 bit PWM outputs:
And best of all, their calibration phase can simply be achieved by flicking
switches at extreme hands positions!

Forecoming issue: compliance with the MIDI protocol (bit-depth, transmission
Pointed out by an article of a QProx concurrent, the Motorola MC33794:
Quoting its author:
"In fact, by slightly raising and lowering my hand, I could see the discrete
quantization steps associated with the MCU’s 8-bit ADC. My hand-waving
experiments would have been better served with a 10- or 12-bit ADC (or an
external programmable amp)."
I'll expand my theory on it later (written long enough for the moment)...

After all, the heterodyning principle (i.e. getting the sum and difference of
two oscillators at close frequencies) was used on the original Theremin only due
to accidental manipulations: during military ham radio tweakings!
The trademark "beating" sound followed up...

Dave Robillard wrote:
> I don't really see what your Theremin-style MIDI controller has to do with
> the synth. It's a MIDI controller, it's seperate from all that stuff by 
> design.

I share your point of view. I just wanted to stay open-minded to prospective
other users, who would justify the need of a live use...

> I'd just write a program to do it.  If you really think a nice little DSP box
> would be useful, do that later. You've got enough problems on your hands 
> building the controller. One step at a time. ;)

Using laptops or sub-multipleITX PC's on the stage will certainly be more
familiar by the time...

Frank Barknecht wrote:
> You can use a whole bunch of input methods in Pd: Midi, score following with
> the fiddle~ external (play on your theremin and feed the audio into Pd, 
> fiddle~ converts it to frequency values), USB over the event interface on 
> Linux, parallel port, serial port input, joystick, probably many more. Pd is 
> quite a happy to speak with anybody.

PureData can already start the software compatibility list then!

Christian Frisson (who *shivers* when hearing Theremin sounds)

More information about the Linux-audio-dev mailing list