Abstract: A system for converting a speech signal into a data signal for controlling an implantable stimulation electrode array hearing prosthesis. An input speech signal is passed through three circuit arms, comprising filter circuits, zero crossing counter circuits and RMS measuring circuits (3-13), for producing signals representing amplitude and frequency of the fundamental voicing component and the first three formants of the speech signal. Computer (14) is programmed with a patient's psychophysical data, and determines the manner of stimulation of the electrodes by ranking the sharpness of the electrodes and assigning sub-bands of the second formant frequency range to particular electrodes. Also, the voiced or unvoiced nature of the signal is determined by comparing the fundamental and second formant components. The output signal passed through a data formatter (15) and transmitter (16) has both formant and prosodic information whereby the production of confusing percepts is avoided.