Harmonic+noise coding based on the characteristics of human phase perception

This paper presents a variable-rate harmonic+noise coder for high-quality coding of speech at an average bit rate of 1.98 Kbps. The proposed coder employs an efficient phase coding technique that reduces the number of bits for phase quantization by taking account of the characteristics of human phase perception. The proposed perceptual phase coding technique takes advantage of the poor phase sensitivity of the human auditory system in the frequency region below the critical phase frequency and in the unvoiced band. The number of bits for quantization of the frequency deviations is assigned according to a perceptual weighting function which is derived from the measurements of just-noticeable difference of phase. Speech quality of the harmonic+noise coder is improved significantly by employing the proposed phase coding technique. Experimental results show that the proposed coder outperforms the 2.4 Kbps sinusoidal transform coder.