Efficient mixed excitation models in LPC based prototype interpolation speech coders

This paper presents a new and efficient method for modeling voiced, mixed excitation spectra in sinusoidal (SC) and prototype interpolation coding (PIC) systems. Speech harmonics are classified as “weak-voiced” or “strong-voiced” by simply examining the short-term residual magnitude spectrum. This information is encoded effectively in terms of fixed width frequency bands and is used to control sets of periodic and random sine wave oscillators which model the short-term mixed excitation nature of speech. In this way the model allows the mixing of periodic and random signal energy on a harmonic basis. The proposed methodology has been used in a 2.4 Kbits/sec speech coder, whose recovered speech quality is better than that of the 4.8 Kbits/sec DoD standard