Researches On Effects Of Phase Features On Mandarin Reconstruction And Music Perception

The current cochlear implant(CI) has poor performance on tone perception and music perception. The essence of tone is the general pattern of the pitch variation. The music melody is made up of different pitches in certain arrangements. They both have the variation of pitch. Acoustic signal mainly includes three characteristics, including amplitude, frequency and phase characteristics.Amplitude and frequency characteristics in cochlear implant coding strategies are fully considered, while the corresponding phase characteristics are often ignored. The relationship between the phase characteristics and tone perception(including melody perception) is worth studying.The article use the method of signal analysis and reconstruction,the technology of short-time Fourier transform and the evaluation of subjective listening. Several researches about the relationship between pitch perception and phase characteristics are presented. (l)Results show that, when classic window size is used and the signal is reconstructed by the original amplitude spectrum and all corresponding zero phases, there is no significant fall in the recognition rate of the new syllable although its sound quality gets worse. However, the original four tones perception is almost lost, about 90% reconstructed syllables are recognized into’flat’ tone or tone 1.Another result shows that, when the signal is reconstructed by the original amplitude spectrum and all corresponding uniformly distributed random numbers of phase characteristics, there is slight fall in the recognition rate of the new syllable although its sound quality gets worse,but the original four tones perception can be identified.It is demonstrated that phase characteristics significantly affects tone perception.(2)Four tones of the reconstructed syllables can be identified again when the window size is reduced to 1 or 2 milliseconds.It shows that the temporal resolution of the signal can can make up for the impact of zero phases.(3)Further sound chimeric reconstruction method, which is cross chimericing and reconstructing from different the same amplitude characteristics and different phase characteristics of syllables.The tone recognition results present that the perceptual tone as 1 to 4 mainly come from the phase characteristics of the chimeric sound.It shows that four kinds of tone perception mainly depend on the phase characteristics. (4)In order to study the relationship between melody perception and phase characteristic,two experiments,including zero phase experiment of commonly used window and variable window are carried out.Results show that, when classic window size is used, the Music melody recognition is almost lost, mostly recognized into’flat’.The melody can be identified again when the window size is reduced to 1 millisecond,while the quality of melody becomes poorer.It shows that the phase characteristics do affect the recognition of music melody, The temporal resolution of music also can make up for "level" phenomenon when phase characteristics are missing.Our conclusion is that, for the reconstructed mandarin syllable, the phase characteristic is dominant to the tone perception and related to the reconstruction window size.The improvement methods for improving pitch perception in CI are pointed out basing on the above research conclusion.Reducing the artificial cochlea electrode stimulus intervals(or increasing the stimulation rate of electrode),sound and tone recognition can be improved without phase characteristics in CI coding strategy. Finally,a summary of experiments improvement suggestions and a future landscape in application of CI is presented.