A study on a reduction of the transmission bit rate by U/V decision using LSP in the CELP vocoder

In typical CELP vocoder, the unvoiced speech is processed like the voiced speech. Hence the speech quality is degraded. Also, the degree of the speech quality degradation is excessive depend on performance of U/V classifier. In this paper, we propose a new U/V (Unvoiced/Voiced) decision algorithm minimized error rate and preprocessing computation. This U/V classifier uses the LSP (Line spectrum Pair) parameter, which is acquired spectrum analysis process in CELP vocoders. Applying this method to the 5.3kbps ACELP, we can get the transmission bits rate reduction of 5.6%(280bps) approximately. As applying the synthesis speech quality in the G.723.1 and the proposed method to the MOS (Mean Opinion Score) test, the former gets average MOS 3.77 and the latter does 3.75.