In CI signal coding, in order to improve the perception of CI user’s music, Professor Tian Lan's research group proposed an all-phase filter design that can preserve more fine sound structure and improve sound quality, especially for music signal. Comparing with classical Butterworth filter bank adopted in CI processors, the objective waveforms and spectra show that the output signal from APDFT filter bank is higher similarity to the original sound. For the normal-hearing (NH) listener, the simulation CI synthetic speech and music by the APDFT filter bank have both higher quality, and perceptual tests on six NH listeners primarily verify the improvement of intelligibility in noise. Thus, the APDFT filter improves the CI hearing quality and will be applied in CI design.

The research was firstly published in the "ICASSP07" conference proceedings with title "The application and computer simulation of multi-channel cochlear implant base on all phase DFT filter".