A phase generation method for speech reconstruction from spectral envelope and pitch intervals

摘要

We propose a new speech reconstruction method from spectral envelope and pitch intervals, which is applicable to the network side of a distributed speech recognition system as a play-back function. The spectral envelope of speech is represented as a set of Mel-frequency cepstral coefficients (MFCC) that is a well-known recognition parameter. First, a sinusoidal synthesis with a zero-phase model is used to obtain a pitch-based waveform. To enhance the naturalness of the speech, we replace the zero phase information with prestored linear and random codebooks. The ultimate phase information is determined depending on the energy ratio between linear and random components. Unlike the classic low bit rate speech coding, however, the energy ratio is estimated in the decoding stage from a time-frequency filter applied to the pitch-based synthesized signal. Thus, the phase information is not a feature parameter from the encoder side. The proposed phase generation method uses the knowledge that pitch variation is a main cause of the mixed characteristics in speech signals. An informal listening test verifies that the quality of the proposed method is much better than that of the synthetic quality.