Analysis-by-synthesis low-rate multimode harmonic speech coding

This paper presents an analysis-by-synthesis multimode harmonic coder (AbS-MHC) that employs new techniques to improve both the speech model accuracy and the parameter estimation robustness in the low rate harmonic coding framework. To improve the speech model accuracy, an enhanced frequency domain transition model is used in conjunction with the sinusoidal model based harmonic coding of voiced/unvoiced speech signals. To achieve robust parameter estimation, a generalized analysis-by-synthesis parameter estimation scheme in the harmonic coding framework is proposed. This scheme uses a time scale signal modification technique to allow for waveform matching in harmonic coding. This concept is demonstrated in our AbS-MHC coder with a specific method for efficient closed-loop pitch estimation and speech classification. The speech quality of the unquantized AbS-MHC coder is better than the 6.3 kbps G.723 quality.