Binary Pulse Excitation: A Novel Approach to Low Complexity CELP Coding

Abstract

The last decade has witnessed an acceleration in the evolution of speech coding. Near-toll quality speech coders are now available at bit rates from 4.8 to 8 kbit/s. These low bit rate speech coders are becoming increasingly needed for many future applications such as digital mobile radio telephony, mobile satellite links, and the emerging ISDN service. High quality speech at these low bit rates has become possible with the introduction of a new generation of speech coding techniques known as analysis-by-synthesis predictive coding. The structure of this new generation of speech coders first appeared with the introduction of multi-pulse excited linear prediction coder (MPE-LPC) by Atal in 1982 [1]. Since its introduction, the MPE has received much attention from researchers, and as a result, several analysis-by-synthesis coders have been developed in the bit rate range from 4.8 to 16 kbit/s with different levels of complexity [2]. These systems include the regular-pulse excited LPC (RPE-LPC) [3], the code-excited LPC (CELP) [4], and the self-excited LPC [5] (or Backward Excitation Recovery (BER) [6]). All the above mentioned coders exhibit the same structure as the originally proposed MPE-LPC [1] in which the excitation signal is optimized by minimizing the perceptually weighted error between the original and synthesized speech. They differ only in the way the excitation signal is defined and coded.