For the auditory sense, voice fundamental frequency information is also provided. Here, voiced speech is represented by a frequency and amplitude controlled sinusoid, and voiceless speech by a random noise with a spectrum and dynamic range matched to the user's comfortable hearing area. They are designed to convey temporally encoded speech information that is psychoacoustically matched to the temporal processing capabilities of residual hearing. Variations in both voice fundamental frequency and speech amplitude contribute the prosodic information that is required for the effective perception of connected speech, but were found not to contribute significantly to the identification of English consonants. For the tactile sense, voiced and voiceless excitation and the associated amplitude envelopes are represented by two vibrators.
Voiceless excitation is detected by a spectral-balance comparator.
However, its precision in fundamental frequency estimation was poorer that these other methods. This finding led us to develop and implement a post-processing buffer that significantly improves the ANN performance by comparing voice fundamental period estimates with immediately prior period estimates, and adjusting the algorithm's thresholds to favour estimates that are similar to recent estimates. The box and whisker plot shows the median, interquartile range and range excluding outliers. A bimodal version of the aid capable if simultaneous acoustic and tactile stimulation will be used in trials later this year. The acoustic aid is also being used for field trials in Beijing for profoundly hearing impaired speakers of the Mandarin Chinese tone language, for whom a fundamental frequency extracting aid is expected to have especial value.