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. 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 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 a quantized signal perceptually closer 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.