Linear predictive speech coding at 2400 b/s

In this paper the salient design criteria are discussed for the developement of a full duplex 2400 bit/second LPC Vocoder. The results of intelligibility tests as well as tests including background noise are described. A frequency domain technique, to improve the quality of LPC-coded speech at 2400 b/s, is also discussed. The aim of the latter technique is to investigate the possibility of coding the prediction residual of a Linear Predictive Coder and still retain a coding rate of 2400 b/s. Use is made of vector quantisation of the DFTs of the prediction residual. The effect of different size code books on the mean square quantisation error is indicated. Compared to a CELP coder this is an interesting alternative, as CELP coders are normally not used below 4,8 kb/s.