Apparatus for analyzing a complex waveform containing pitch synchronous information

Abstract

Abstract 1,139,711. Speech recognition. STANDARD TELEPHONES & CABLES Ltd. 30 Nov., 1966, No. 53636/66. Heading G4R. In apparatus for analysing a complex waveform, the waveform is fed via a band-pass filter to a zero-crossing detector and a peak amplitude detector, the time elapsed between two successive zero crossings bearing a specific relationship to the detection of a peak amplitude being obtained. In Fig. 2, a speech waveform is band-pass filtered at 7 before passing to a peak amplitude detector 8 and zero-crossing detector 9. The first peak, detected at 8, switches on a counter 11 so that it counts zero-crossings, detected at 9. The first zero-crossing also starts an integrator 14, 15 which is read out via AND gate 16 to a sample and hold circuit 17 on a count (at 11) of two. Thus circuit 17 stores a voltage proportional to the time elapsed between the first and second zero-crossings following the first peak. Circuit 17 may feed an oscilloscope and is reset at the start of the next voicing cycle, or when threshold circuit 18 indicates an absence of signal. In Fig. 4, four circuits 20, 21, 22, 23 each as above, the filters having the pass-bands shown, are used to recognize the presence of the first and second formants. If the outputs of circuits 20 21, 22, 23 exceed respective thresholds, the ratio of the thresholds being fixed but the actual magnitudes depending on a master threshold circuit 24 responsive to the speech input, "threshold yes" outputs are energized. Units 25,27,29,31,32 and AND gates (some inhibitory) and units 26, 28 are OR gates. Coincidence unit 30 produces an output if its inputs are unequal. Fig. 4 is otherwise self-explanatory.

Inventors

• 👤 Robert Walter Alister

Bibliographic Details