Perceptual phase quantization of speech

It is essential to incorporate perceptual characteristics of human hearing in modern speech/audio coding systems. However, the focus has been confined only to the magnitude information of speech, and little attention has been paid to phase information. In this paper, a quantitative. study on the characteristics of human phase perception is presented and a novel method is proposed for the quantization of phase information in speech/audio signals. First, the just-noticeable difference (JND) of phase for each harmonic in flat-spectrum periodic tones is measured for several different fundamental frequencies. Then a mathematical model of JND is established based on the measured data, to form a weighting function for phase quantization. Since the proposed weighting function is derived from psychoacoustic measurements, it provides a novel quantization method by which more bits are assigned to perceptually important phase components at the sacrifice of less important ones, resulting in perceptually closer quantized signal to the original one. Experimental results on five vowel speech signals demonstrate that the proposed weighting function is very effective for the quantization of phase information.