Speech analysis through formant detection

Abstract

Abstract 1,245,414. Speech analysis. INTERNATIONAL BUSINESS MACHINES CORP. 10 Sept., 1968 [14 Sept., 1967], No. 42905/68. Heading G4R. Sound analysing apparatus comprises a plurality of filter systems, each of which has an output of amplitude and phase corresponding to a respective frequency band of an input sound signal, a threshold system for each filter system for determining which filter system output is above a predetermined threshold, and control means for varying this threshold independently of the instantaneous value of an input sound signal. A speech waveform at 1 is split into frequency bands by phase filters 2a-n, each of which produces an output the phase of which depends on the difference between the frequency of the input and the centre frequency of the filter, the outputs being limited at 4a-n and compared in quadrant detectors 6a-n with the original speech waveform limited at 8. Each quadrant detector produces a 2-state output, the upper state occurring when both inputs exceed a threshold. The quadrant detector outputs, after low-pass filtering at 8a-n for averaging, set respective threshold latches 14a-n if they, added to a ramp voltage from ramp generator 12, exceed a threshold. Each threshold latch 14a-n which is set, sets a corresponding formant latch 19a-n, via logic circuitry 16a-n, 17a-n, provided the two adjacent threshold latches (if any) are not set. The number of formant latches set is counted by a counter 22. A predetermined count resets the ramp. A sample clock 10 produces timing signals, the start of each of which permits the ramp to start, and the end of each of which resets the ramp if it has not already been reset by the counter 22. The counter 22 and threshold latches 14a-n are reset at the end of each timing signal.

Inventors

• 👤 Howard W Cotterman
• 👤 John H King Jr

Bibliographic Details