Real-time implementations and applications of the US Federal Standard CELP voice coding algorithm

The author describes two real-time implementations of the US Federal Standard 1016 (USFS-1016) CELP (code excited linear prediction) V3.2 4800 b/s voice coding algorithm. A floating-point implementation for the TI TMS320C30/C31 and a fixed-point implementation for the TI TMS320C25/C51 are described. The floating-point system implements the full 1016 standard including a 512 stochastic codebook search and fractional pitch search. Results from subjective listening tests are presented which show the implementation to perform as well as or better than the USFS 1016 FORTRAN simulation. A 7200 b/s land mobile radio (LMR) system that augments the floating-point vocoder with 2400 b/s channel error coding has also been implemented and is described. The performance of the LMR system in various channel scenarios is presented in the form of error detection and correction performance. Furthermore, parallels are drawn and developed between the LMR system and a typical tactical voice communications system. A miniature vocoder system is also presented