High Quality Speech Coder at 300 bit/s
Qiang Guo · Audio Engineering · 2010
A vocoder to obtain high quality synthetic speech at 300 bit/s is presented based on mixed excitation linear prediction(MELP) which extracts only few parameters each frame.To obtain high quantization efficiency,vector quantization is performed on parameters of the super-frame composed by eight frames.The quantization efficiency of band pass voicing coefficients(BPVC) is improved based on estimation using code-book mapping over mode transition.Codebook sizes of pitch parameter for different unvoiced/voiced model are jointly optimized to improve the quantization efficiency.Meanwhile,multi-stage vector quantization with inter-stage prediction is perfor-med for linear spectral frequency parameters(LSF) to reduce the spectral distortion.Simulation results show that the intelligibility of this 300 bit/s vocoder is quite good and the natural tone is fine.The diag-nostic rhyme test(DRT) score is 84.2%.