Improved Speech Coding Strategy Based on Wavelet Transform Zero-Crossings for Cochlear Implants

To enhance the performance of speech coding strategy of cochlear implants, wavelet transform zero-crossings stimulation (WZCS) strategy based on one-octave wavelet transform is presented. Zero-crossings of processed signal were derived in the domain of wavelet transform and further the amplitude of signals was modulated by corresponding temporal envelope to form the synthesized stimulus. Four strategies of WZCS, continuous interleaved sampling (CIS), channel specific sampling sequences(CSSS), frequency amplitude modulation encoding(FAME) were simulated using Matlab. Correlativity analysis between synthesized stimuli and original signal, also between their spectra and that of original speech, was implemented. Compared to other 3 strategies, WZCS obtains the highest correlation coefficient between spectrum of synthesized signal and that of original speech, that is to say, the spectrum of synthesized signal through WZCS strategy is the most correlated to that of original speech. The algorithm presented in this paper keeps more frequency components and phase information of original speech in synthesized stimulus compared to other strategies.