Very low bit-rate F0 coding for phonetic vocoder using MSD-HMM with quantized F0 context

This paper presents a very low bit-rate F0 coding technique for speaker-dependent phonetic vocoder based on hidden Markov model (HMM) using quantized F0 context. In the proposed technique, the input F0 sequence is converted into F0 symbol sequence at a phoneme level using scalar quantization. The quantized F0 symbols are used in the decoding process as the prosodic context for the HMM-based speech synthesis. The synthetic speech is generated from the context-dependent labels and input speaker´s pre-trained HMMs by using the HMM-based parameter generation algorithm. By taking account account of preceding and succeeding phonemes and F0 symbols as the contextual factors, we can generate smooth F0 trajectory similar to that of the original with only a small number of quantization bits. Experimental results demonstrate that the proposed technique can generate F0 contour with acceptable quality even when the bit-rate is less than 50 bps.