Implementation of a multi-pulse speech codec with pitch prediction on a single chip floating-point signal processor

The multi-pulse speech coding with pitch prediction has been known as an efficient speech coding technique for coding speech at a bit rate of 8 to 9.6 kbps. To implement this coding method on a signal processor for real time applications, problems exist concerning the amount of computations, speech quality, and the data RAM size on a signal processor. As countermeasures against these problems, we propose: 1) Correlation computation amount reduction method by utilizing pitch periodicity of the impulse response, 2) Pulse search method to modify pulse amplitude by only a small amount of computations in order to improve speech quality, 3) Efficient use of the memory space of a signal processor. These methods made it possible to implement a 8 to 9.6 kbps multi-pulse speech codec with pitch prediction with an optimum analysis frame length of 20 ms on a single chip 32-bit floating point signal processor (µPD77230).