DCT_M model for excitation parameter in low bit rate vocoder

Abstract

The description precision of an excitation signal greatly influences the quality of reconstructed speech in low bit rate vocoders. To improve the reconstruction quality, the DCT_M model is proposed to express the excitation spectral parameter, which transforms the variable length vector to fixed dimension vector through DCT transformation. It then quantizes the fixed length vector using multi-stage vector quantization. Tests show that the proposed method can keep the shape of the entire spectral envelope and reduce model error thus greatly improve the description precision. Test results in the sine excitation linear prediction (SELP) vocoder show that the DCT_M model can improve the naturalness of reconstructed speech, with subjective test score of 65%.

Keywords

vocoder / DCT_M model / model error