Combined Estimation/Coding Of Highband Spectral Envelopes For Speech Spectrum Expansion

This paper addresses the problem of expanding the bandwidth of narrowband speech signals focusing on the estimation of highband spectral envelopes. It is well known that there is not enough mutual information between the two bands. We show that this is happening because narrowband spectral envelopes have an one-to-many relationship with highband spectral envelopes. A combined estimation/coding scheme for the missing spectral envelope is proposed, which employs this relationship to produce a high quality highband reconstruction, provided that there is an appropriate excitation. Subjective tests using the TIMIT database indicate that 134 bits/sec for highband spectral envelope are adequate for a DCR score of 4.41. This is an improvement of 22.8% over a typical estimation of highband envelopes using usual mapping functions, in terms of DCR score.