FR2127345A5 - - Google Patents

Abstract

1344019 Vocoder excitation generator INTERNATIONAL BUSINESS MACHINES CORP 27 Jan 1972 [25 Feb 1971] 3793/72 Heading H4R In a speech synthesizer in which a low frequency portion of the speech spectrum is transmitted and distorted to derive an excitation signal for synthesis of a higher frequency portion of the speech spectrum, zero crossings of the waveform in a particular direction are detected and pulses generated, each of which represents by its amplitude or duration the time interval between a pair of successive zero crossings. In an analogue embodiment positive going zero crossings of the low frequency portion of the speech cause triggering of a sawtooth generator tile output from which is differentiated to provide pulses, generated during the flyback period, of constant amplitude whose width is dependent on the excitation frequency. In an alternative embodiment, Fig. 4(a), operating digitally, the sign of the low frequency band of the speech signal is fed to an exclusive or gate XOR both direct and via a one clock pulse delay T1 to derive pulses on each of the zero crossings. Combination with the original signal, SIGN, in AND1 provides pulses only on positive going zero crossings which are used after a delay T2 to reset a counter CO, which provides a staircase signal on its output. The undelayed pulse is used to sample the staircase just before resetting so that the output S is a pulse whose amplitude is dependent on the time elapsed since the previous resetting, and hence the excitation frequency.