Speech analysis system

Claim 1

In a speech analysis system comprising means for converting an input analog speech signal into a digital speech signal, means for storing segments of said digital speech signal, means for transforming each segment into a sequence of spectrum components, which means comprise means for performing a discrete Fourier transformation, whereby a series of amplitude spectrum each consisting of a sequence of spectrum components is produced, a bistable indicator settable to indicate a period of voiced speech and resettable to indicate a period of unvoiced speech or the absence of speech, and programmable computing means programmed to carry out the process including the steps of: determining for each segment (number I) the peak value (M(I)) of the spectrum components of the relevant amplitude spectrum in a low frequency band of about 200-800 Hz, determining, if said indicator is set, for each segment and a number of preceding segments the maximum value (VM(I)) of the peak values M(n), with n=I, I-1, . . . I+1-m, in which m is such that between segments I and I+1-m there is no change in the state of the indicator, determining for each segment an adaptive threshold (AT(I)) by setting AT(I) equal to a fraction of the maximum value VM(I) if said indicator is set and by setting AT(I) equal to a fraction of AT(I-1) if said indicator is reset, setting the bistable indicator if the peak values M(n) with n=I, I-1, . . . I+1-k, wherein k is a predetermined number, increase monotonically for increasing values of n, by more than a given factor and M(I) exceeds the adaptive threshold AT(I-1), and resetting the bistable indicator if the peak value M(I) is smaller than a given fraction of the maximum value VM(I-1) or is smaller than a predetermined threshold.