Programmable Digital Speech Processor for Auditory Prostheses

Auditory Prostheses is an electronic device that partially replaces the functions of the human ear. Unlike a hearing aid, it does not make sound amplification or filters the noise signal but instead bypasses normal hearing operation to directly stimulate the auditory nerve with electric current allowing hearing impaired persons to receive sound. The function of Auditory Prostheses is an artificial replacement of damaged inner ear using external Body Worn Speech Processor (BWSP) and internal Receiver-Stimulator (cochlear implant) for stimulating auditory nerve via electrode array that enables understanding the speech by brain. Speech processor receives an external sound or speech and generates encoded speech data bits for transmission to receiver-stimulator via Radio Frequency transcutaneous link for excitation of electrode array. Development of the Programmable Digital Speech Processor for Auditory Prostheses (PDSPAP) is based on the Analog Devices Digital Signal Processor ADSP-2185 is described. The Dallas DS89c450 microcontroller is used as data encoder to send speech information from speech processor to receiver-stimulator via RF transcutaneous link. The complete Auditory Prostheses system contains two parts Body Worn Speech Processor and Cochlear implant. The BWSP comprises analog front end (AFE), a Digital Speech Processor, Microcontroller based Data Encoder, a Radio Frequency Transmitter using Amplitude Shift Keying (ASK) modulation. The Cochlear Implant system consists of ASK receiver, Receiver-Stimulator, and an Electrode Array of six electrodes. One of the efficient Speech Processing algorithm Continuous Interleaved Sampling (CIS) speech processing algorithms is implemented for the Speech Processor and it can be programmed to develop and test 4-channle to 8 channel CIS algorithm based on the patient’s available active electrodes. The output of the Speech Processor is a continuous ASK modulated signal with 4MHz carrier and serial TTL data bits as modulating signal. The serial TTL data bits correspond to the processed incoming speech/sound signal. The ASK signal is applied to the RF transcutaneous link that in turn stimulates the Cochlear Implant/Receiver-Stimulator available as Laboratory model. Finally some results for sample speech signal - “Hello” such as, output of Speech Processor as ASK signal and stimulating signal at simulated electrode resistance array that corresponds to artificial hearing sensor array in the damaged inner ear.