8 kbit/s short and medium delay speech codecs based on CELP coding

This paper discusses two speech-coding algorithms at around 8 kbit/s. These algorithms both use pre-selection in the codebook search and training for the conjugate structured random codebook. One has short-delay time that can dispense with echo-control equipment. This algorithm is robust against channel errors by using LPC analysis separated from pitch excitation, although LPC parameters are derived from the locally decoded signal. The other algorithm has medium-delay time and meets all the requirements of the ITU-T (formerly CCITT) 8 kbit/s speech coding standard. The performance of these codecs is evaluated using signal to noise ratio (SNR), pair comparison tests with a modulated noise reference unit (MNRU), and Mean Opinion Score (MOS). The major applications of these codecs are personal handy phone systems and FPLMTS.