engleski

The effects of sound coder carrier rate and modulation bandwidth on voice pitch perception in CI users

We employed the dual filter-bank “STEP” coder to separately control the spectral and temporal modulation resolution of analysis channels. Previously we compared vowel pitch ranking and gender classification with eight subjects using enhanced modulation at F0 - including across- channel synchronised modulation - to the standard clinical ACE coder: Using standard moderate carrier rates (900 to 1200 pps / channel) there was no significant improvement using modulation enhanced coding versus ACE across subjects. Neither poorer nor better performers on either task obtained a benefit from enhanced F0 modulation in the range 120 to 210 Hz. In a follow-up experiment we looked at the effect of stimulation rate on voice pitch perception. Since there are large inter-subject differences in overall temporal pitch acuity we hypothesised that some subjects’ performance may be more greatly influenced by carrier rate than others, or that some subjects may find sound quality satisfactory with lower carrier rates than those in their clinical processors. We used a version of STEP with a very short temporal envelope analysis window of 2 ms which allows a very low latency real-time processing implementation and large maximum modulation bandwidth. Subjects were tested using carrier rates of 1000, 500 and 250 pps/ch with modulation bandwidths controlled via low-pass filtering. Pilot testing indicated that the new low-latency coder provides very good sound quality compared to clinical ACE using 1000 pps/ch or 500 pps/ch. In addition the modulation bandwidth could be tuned at different carrier rates to optimize voice pitch perception based on temporal cues. This opens the potential for lower stimulation rates to be used in CI sound coding while maintaining optimal temporal resolution. More data will be available at the meeting. Acknowledgments: This research was supported by Cochlear, and a part of the work by DK was funded by the European Commission (FP7-CIG-2011- 303927).

cochlear implant ; pitch perception ; voice gender

nije evidentirano