Narrowband to wideband conversion of speech using GMM based transformation

Reconstruction of wideband speech from its narrowband version is an attractive issue, since it can enhance the speech quality without modifying the existing communication networks. This paper proposes a new recovery method of wideband speech from narrowband speech. In the proposed method, the narrowband spectral envelope of input speech is transformed to a wideband spectral envelope based on the Gaussian mixture model (GMM), whose parameters are calculated by a joint density estimation technique. Then the lowband and highband speech signal is reconstructed by the LPC synthesizer using the reconstructed spectral envelope. This paper also proposes a codeword-dependent power estimation method. Both the objective and subjective test results shows that the proposed algorithm outperforms the conventional codebook mapping method.