DCELP: a low bit rate and low delay speech coding method

Methods for obtaining high quality speech at very low bit rates have become very important in the digital communication environment. Good quality speech has been reported at bit rates as low as 2.4 kb/s. Apart from the bit rate, another important consideration is the delay due to the coding methods used. For applications like digital telephony, a one way delay of less than 2 ms is required for ease in echo cancellation. Low delay methods have been developed; however, these work at much higher bit rates than methods with high delay. The authors present a method that can be used to obtain good quality speech at a bit rate as low as 2.66 kb/s and a delay of less than 2 ms. The method, termed differential code excited linear prediction (DCELP) is a CELP based method differing from other CELP variations in that a low delay version of CELP is used to code the error signal rather than the actual speech signal. DCELP is a vector based system comprising two main blocks, a vector predictor and CELP acting as a vector quantizer