GENWiki

P  R  D  X  L

A PARADOXICAL SOUND SYNTHESIZER
by Thierry Rochebois 1/2/94
   email: thierry@marion.ief-paris-sud.fr

Paradoxical Sounds

The main property of paradoxical sounds is that
their frequency do not change when you go an
octave higher. This property is achieved thanks
to an appropriate spectrum modelling as shown
in the picture file paradoxi.gif.

PRDXL

Prdxl is a wave table paradoxical sound synth.
I built a basic prototype of this synth this
summer.
Its schematics are shown in the picture file
prdxl.gif. The EPROM is filled with the 12
paradoxical tables. Its contents can be found
in the file prdxl.hex: an hex code per line
in ASCII format (32k lines). I hope that every
EPROM programmer can read this kind of raw 
file format.

The schematics can be divided in two parts:

THE KEYBOARD ENCODER

  It encodes the 12 keys in a 4 bit format and
  generate a gate signal.
  This is not the most interesting part of the
  schematics.

THE WAVE TABLE READER

  It reads the wave table addressed by the 4
  bit key code. A dac transforms the binary
  output data into analog signal.
  This is the must interesting part to build
  (you can test it by simulating the 4 bit
  key code and the gate signals with switches,
  but playing music in binary code is not very
  easy!). A basic envelop is implemented as
  a capacitor on the ref voltage pin of the
  DAC, you can improve it by using a true
  ADSR and a true VCA (or by using modules
  of the synth you own).

Nota: these schematics are basic and can be
improved by adding modules such as filters,
ADSR,VCA, sequencer and so on.