An alternative way to encode voicing in multichannel cochlear implants

Voicing is the feature that indicates whether a speech sound is quasiperiodic or aperiodic. It is used perceptually to discriminate pairs of sound such as /s,z/,/p,b/,f,v/, etc. The nucleus WSP-III multichannel speech processor uses a stimulation rate equal to the fundamental frequency of the input speech signal: two pulses are sent in rapid sequence during each fundamental period. When speech is unvoiced and a fundamental frequency cannot be determined, a random stimulation rate of approximately 100 Hz is used. Therefore the processor uses the stimulation rate to encode voicing: unvoiced sounds are delivered using a random rate while voiced sounds are delivered using a more stable rate. The author´s compare this voicing encoding strategy to a novel one which uses an extra pulse per period when voicing is present in the input signal. Results were encouraging: one subject achieved 100% discrimination with the new strategy (after very limited training), compared to 85% obtained using the old strategy.<>