[Speech coding strategy based on amplitude and frequency modulation for cochlear implants].

To enhance speech recognition in noise, as well as tone recognition, we presented a new kind of speech coding strategy, called one-octave wavelet transform zero-crossing stimulation (WTZS), for cochlear implants based on amplitude and frequency modulation. We selected 15 volunteers with normal hearing ability to carry out hearing simulation experiments by picking up the amplitude (amplitude modulation, AM), zero-crossings (frequency modulation, FM) and gradient parameters from processed speech signal in the domain of one-octave wavelet transform to synthesize the stimulating pulstile series. The experimental results demonstrated that the phonetic recognition in quiet surroundings with amplitude modulation only strategy (CIS) is similar to that of amplitude and frequency modulations strategies (FAME and WTZS), while the tone perception of CIS is inferior to that of FAME and WTZS strategies. However, in noisy environment, the phonetic recognition, tone perception, as well as sentence recognition of WTZS strategy are better than those of CIS and FAME strategies. WTZS strategy, utilizing amplitude (AM), zero-crossings (FM) and gradient parameters to synthesize stimulus, can enhance the phonetic and tonal language recognition in noise environment effectively, and could be used in cochlear implant system for speech processor design after arithmetic optimization.