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Design and testing of time-varying inductors and capcitors for an electrical speech synthesizer Wickwire, Kenneth Freeman

Abstract

This thesis describes the design and testing of time-varying inductors and capacitors for use in an electrical analogue of the human vocal tract. The inductors and capacitors were varied in accordance with an external control signal by varying the value of a resistor in a circuit which used operational amplifiers to simulate a variable impedance. The inductor actually tested is not a true inductor, since its voltage e and current i are related by the equation [formula omitted], where L(t) is an externally controlled time function. A device for which [formula omitted] will probably be adequate for use in a vocal tract analogue. A true inductor for which [formula omitted] can be realized by making a change in the circuit tested. For the inductor tested, the maximum allowable input voltage and current are ± 2 volts and ± 2 ma, respectively. For the capacitor, the allowable ranges are ± 4 volts and ± 20 ma. The inductance and capacitance can be varied over a range of 250:1 with good linearity with respect to external control voltage and audio frequency. The inductor's Q exceeds 50 and the capacitor's Q exceeds 200 for all frequencies between 200 Hz and 5 KHz. A system for routing control signals from a digital computer to the vocal tract analogue has been devised. Each component in the analogue is to be serviced by the computer at discrete time intervals. Between computer service times, the value of each component is interpolated by the up-down counter-digital comparator interpolating system described in the thesis.

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