Speech processing method and apparatus

Abstract

Signal processing system for converting a speech signal into a data signal for controlling a hearing prosthesis having an implanted electrode array adapted to stimulate the auditory nerve fibers of a patient by the application of electrical currents to selected electrodes in the array. The system generates an input signal current corresponding to a received speech signal. The amplitude and frequency of the fundamental voicing component of the speech signal is approximated as are the amplitude and frequency of at least one formant of the speech signal. A programmable microprocessor produces instructions which cause the application of electrical currents to selected groups of electrodes in the array with or without delays between the stimulation of each electrode in the groups. The microprocessor is programmable with data defining a predetermined relationship between each group of electrodes and a selected range of at least one formant frequency and with data defining a predetermined relationship between another formant frequency and the delay between stimulation of each electrode in each said group based on psychophysical testing of the patient. Selection of electrodes based on the estimated frequency of the formants produces the desired percepts in the auditory-like sensations generated in the patient. The microprocessor is further programmable to produce data which determines the level of stimulation of each selected group of electrodes and determines the delay between stimulation of electrodes in each group dependent on the estimated amplitude of formants of the speech signal as well as on predetermined data relating to the sensitivity of each electrode implanted in the patient.