In WI coding scheme

how to decompose and quantize the characteristic waveforms with low delay

low complexity and high precision have always been a hot research topic.The characteristic waveform decomposition based on non-negative matrix factorization is proposed in this paper.This CW decomposition method doesn't bring any additional delay to WI coder;In order to improve decomposition precision

the CW is firstly classified according to the maximum pitch of its sub-frames before being decomposed.Besides

band-partitioning initialization constraints are set to basis vectors before NMF is carried out

and this has made the CW decomposition precision of NMF-based method be comparable with that of 2 ranks of SVD;In order to reduce the computational complexity of WI coder

the CW alignment procedure is removed in our NMF-WI coder

and the factorization rank of NMF is set to 16 as a trade-off between computational complexity and decomposition precision.In the end

the low dimensional coding matrix is quantized by splitting matrix quantization scheme.The subjective A/B listening tests show that the proposed 2kb/s NMF-WI coder can give smooth speech with quality close to 2.4kb/s SVD-based WI coder.Mean Opinion Score test results indicate that the performance of proposed coder is a little worse than that of 2.4kbps MELP coder.