Speech analysis system

Claim 1

In a speech analysis system comprising means for receiving an input analog speech signal and means for determining at regularly recurring instants the mean value of the rectified speech signal in segments thereof preceeding said instants, the mean values thus determined providing a measure for separating voiced speech segments from unvoiced speech segments, the provision of 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 mean value (M(I)) of the rectified speech signal of the relevant segment 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 mean 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 mean 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), resetting the bistable indicator if the mean value M(I) is smaller than a given fraction of the maximum value VM(I-1) or is smaller than a predetermined threshold.