Method and system for determining the variation of a speech parameter, for example the pitch, in a speech signal

Claim 1

Method for determining the variation of a speech parameter as a function of time in a speech signal, characterized in that (i) in a first step - time segments of the speech signal are derived from the speech signal at m time instants which regularly follow each other, - and from each time segment i (1≦ i≦ m) there is derived a measure of fit p(i,j) which is associated with the time segment and which, for a series of n possible values for the speech parameter, indicates how well a chosen value f j for the speech parameter (1 ≦ j ≦ n) fits the speech signal of the relevant time segment i, (ii) in a second step for the time instant i = and for each of the n possible values f ; for the speech parameter, a value ms(1,j) associated with said speech parameter, which value is equal to p(1,j) is stored in a memory, (iii) in a third step - for a certain time instant i( >1) and a certain possible value f j for the speech parameter, a number of summation values s h (i,j) are derived in accordance with the formula s h (i,j) = p(i,j) + ms(i-1,h) + k(f j (i),f (i)) where h runs from x up to and including y and for x and y it holds true that 1 ≦ x ≦ j, j, j ≦ y ≦ nand x ≠ Y, - of all the y-x + summation values s h (i,j) the optimum summation value is stored in the abovementioned memory as the value ms(i,j) and, in addition, a coupling vector v(i,j) which refers to the value f h (i-1) of the speech parameter at the time instant i-1, which, for the relevant index h, resulted, according to the above formula, in the optimum summation value, is stored in a memory, (iv) in that the third step is repeated for all the other indices j at the time instant i, (v) in that the third step is repeated for all the indices at a subsequent time instant i + 1, (vi) and in that k(f j (i),f (i)) is. a cost parameter which is a measure of the deviation of the speech parameter f j (i) at the time instant i with respect to a predicted value f (i) for the speech parameter at the time instant i, which predicted value is derived from at least the speech parameter value f h (i-1) at the time instant i-1, and is determined in accordance with the formula where a o is a constant which is less than zero and, if r ≧ 2, f 1 (i-z) is the value for the speech parameter at the time instant 1-z, which value lies on a sub-path which, via the coupling vectors v(i,j), leads to the speech parameter f h (i-1) at the time instant i-1.