Implementation and evaluation of variable bit rates CELP coder

摘要

Speech communication has a central position in human communication. In wireless telephony communication, the goal of speech coding is to represent speech with the possible least number of bits while maintaining an acceptable level of quality. The lower the bit rates the increase of the number of users within the restricted bandwidth. This paper introduces an efficient method of reducing the amount of bits required to transmit with optimum speech quality. According to speech quality of received signal depending on channel condition, a variable bit rate speech coder is implemented to maintain the reasonable speech quality in various channel conditions. Various modes of bit rates are used in the implemented coder. Low bit rate modes are used in a bad channel condition to allow more bits for channel coding, while high bit rate is used in better channel conditions. The speech quality, in terms of variable bit rates, is measured using analytical evaluation.