Developed on the initiative of Alain Daniélou and at his request, and tuned according to his theory, the Semantic is an electronic musical instrument designed by Michel Geiss, Christian Braut and Philippe Monsire. It is the successor of a previous version, the S52, created by Claude Cellier and André Kudelski. The S52 was devised to check the theory, but as an instrument was difficult to play, due to ergonomics. The Semantic has been designed as a complete musical instrument. To make it easier to play, Alain Daniélou decided to utilize only 36 of the 53 notes of the scale (cf. Annex 2), considering the other notes less essential.

The Semantic is a "ready-to-play" instrument, fully self-contained, and user-friendly for composers and musicians. The instrument comprises a Kurzweil K2000 R sound generator and two Midy 20 Cavagnolo button keyboards. A powered amplifier is incorporated to avoid any need for external amplification. The Semantic will offer a choice of twenty or so different tones (the spectrums of which will be designed to highlight Alain Daniélou’s theory). To enhance the performance, the keyboard is velocity-sensitive (speed with which the keys are pressed), as well as aftertouch-sensitive (pressure variations while the keys are being pressed). Furthermore, sustain and expression pedals and faders are provided to produce an effect on volume attack and release parameters, on spectrum, etc.

Among other reasons, the K2000 R was chosen because each note can be tuned to one-cent accuracy. In other words, at the worst, the pitch of a note programmed on this instrument could only deviate by half a cent from its theoretical value - a very low margin of error allowed by Alain Daniélou. By way of example, raising notes C1 (65.406 Hz) and C6 (2093.005 Hz) by one cent corresponds to increasing their frequency by 0.0378 Hz and 1.209 Hz respectively.

As compared to the usual piano keyboard, the button keyboard has two distinct advantages. Firstly, its aspect is sufficiently different from the former which, to the musician’s mind, is synonymous with the tempered scale. It was thought that with a new instrument like the Semantic, it would be better to break away from accepted ideas. Furthermore, with respect to the average finger span, a greater number of notes can be reached than on a piano keyboard, which is essential considering that it has three times more notes than the piano keyboard.

Though, the Semantic comprises two keyboards with 105 keys each, corresponding to a range of almost 6 octaves. At the same time, it is possible to transpose by semitones or octaves. The space required for the 105 keys is a mere 18 by 4 inches. For comparison, one octave on the Daniélou scale takes up 5.2 inches, whereas on a piano keyboard the same number of notes would need 14.4 inches, or nearly three times as much.