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Background noise poses a significant challenge to people who have a cochlear implant for restoring their hearing ability. A cochlear implant can process sound into 12 to 24 channels and it provides limited temporal and spectral information to the auditory nerve through electrical current stimulation. In this paper, a specific noise reduction algorithm was developed to accommodate the need of adaptively applying a small number of gains to the stimulation signals in cochlear implants. A sound signal was first divided into 22 channels using the WOLA (Weighted Overlap Add) spectral analysis. The spectral templates of background noise were estimated by automatically tracking energy gaps between speech segments. The gap detection algorithm utilized a mechanism like the charging and discharging of a capacitor in an envelope detector, which offers the ability for the extracted energy signal to stay at noise floors. The noise templates were updated adaptively when a segment of signal was determined to be noise. Simulations of the proposed noise reduction algorithm were performed using offline processing and it has also been implemented on the Ezairo 7150 (ON Semiconductor Corporation) DSP platform with a WOLA co-processor. Initial evaluation results showed that the signal-to-noise (SNR) ratio can be improved by up to 10 dB after noise removal.

Parameter model methods of power spectrum estimation in electronic signal processing field have been introduced including Levinson-Durbin Method, Burg Method and the latter proposed Covariance Method. The measure of the random processing signal spectrum has been investigated based on the mathematic software MATLAB. The performance of spectrum estimation such as the analyzing of signal frequency, resolution, and side lobe characters has been realized in the research. Different parameter values of method has been compared, conclusions can be made that larger the sampling number is, higher estimation performance will be, and Covariance Method is equipped with a satisfying performance to its counterparts although the appearance of frequency fluctuation in side band.