speak to your computer

speak to your computer elektor november 1981 — 11-45 by David Ridyard B. Sc. Human Speech Before describing the techniques employed in this system it is worth briefly considering the production and form of human speech. The vocal tract can be seen to consist of a d.c. power supply, square wave oscillator and a resonator. The lungs provide a constant air pressure on the back of the taut vocal folds, or vocal chords, which forces these two flaps of skin to open. The Bernouilli forces set up by the air flow then force the folds shut, and the result is a stream of glottal pulses, which may be approximated to a 150 Hz square wave. This means a fundamental at 150 Hz with exponen- tially decaying odd harmonica at 450 Hz, Work on speech has also shown it is quite intelligible when infinitely clipped, that is to say that zero crossing infor- mation is sufficient to characterise a word. This allows us to use a compara- tor to reduce speech to a single serial bit stream, thus eliminating t...