METHOD AND SYSTEM FOR SPEECH RECONSTRUCTION FROM SPEECH RECOGNITION FEATURES

摘要

A speech reconstruction method for converting a series of feature vectors and a series of respective pitch values and voicing decisions of an original input speech signal into a speech signal, the feature vectors being obtained as follows: (i) deriving at successive instances of time an estimate of a spectral envelope SE(i), i being a frequency index, of the digitized original speech signal, (ii) multiplying each estimate of the spectral envelope by a predetermined set of frequency domain window functions, BW(i, k), i being a frequency index and k being the window function index, wherein each window is non-zero over a narrow range of frequencies, and computing the integrals thereof, according to the expression: where BI(k) is defined as the kth component or " bin" of a " binned spectrum" , and (iii) assigning said integrals or a set of pre-determined functions thereof to respective components of a corresponding feature vector in a series of feature vectors; said speech reconstruction method comprising: (a) converting each feature vector into a binned spectrum, (b) generating harmonic frequencies and weights according to the corresponding 1438 א' בתמוז התשס" ד - June 20, 2004 pitch and voicing decision, (c) generating for each harmonic frequency a respective phase, depending on the corresponding pitch value and voicing decision and possibly on the binned spectrum, (d) sampling a predetermined set of basis functions each being a function in a set of frequency domain functions with bounded supports at all harmonic frequencies which are within its support, and multiplying by the respective harmonic weight, so as to produce for each sampled basis function a respective line spectrum having multiple components, (e) combining each component of each respective line spectrum with the respective phase thereof so as to produce a complex line spectrum for each basis function, (f) generating gain coefficients of the basis functions, (g) multiplying the complex line spectrum of each basis function by the respective basis function gain coefficient, and summing up all resulting complex line spectra to generate a single complex line spectrum having a respective component for each of the harmonic frequencies, and (h) generating a time signal from complex line spectra computed at successive instances of time. 1439 א' בתמוז התשס" ד - June 20, 2004