Research On Adaptive Echo Cancellation Technology In Digital Heating Aid

Hearing aids can help patients with hearing impairment to improve their hearing. The goals are the high quality of sound and the miniaturization of the hearing aid. The miniaturization means that the distance between the microphone and the speaker is very close, which results the microphone pick up part of the output signal when the output is received by our ear. The part been received again is just forming echo. The echo limits the maximum stable gain of hearing aids and also reduces the intelligibility and listening comfort of the sound. In order to solve the interference problem caused by the echo in the hearing aid, this thesis will research the adaptive echo cancellation algorithm.In this paper, we insight into the traditional echo cancellation algorithms such as LMS, RLS and NLMS algorithm. The update method of the coefficient of these algorithms is bit by bit and the operation is large. Considering the high requirements of digital hearing aids, the BLMS algorithm is introduced to form the NBLMS algorithm to change the updating way of the filter coefficients and reduce the complexity of the algorithm.Although the NBLMS algorithm can solve the problem of resource waste of the system due to point by point, the NBLMS algorithm also has some problems, such as the convergence effect is not good, the residual is large, and the sound quality is not good. Considering the above problems, the NBLMS_S algorithm is obtained by introducing the estimation error of the current time into the normalized step size. And then the two improved algorithms are designed. The one is to use the idea of the "forgetting factor" in the RLS algorithm and to improve the update process of the filter coefficients which is called NBLMS_MKS algorithm. The other is called by ?VS_BLMS which based on the NBLMS_S. Acorrding to the characteristics of the Sigmoid function, it builds a nonline relation similar to the Sigmoid expression between the estimation error and the variable step size.After the design of the improved algorithms NBLMS_MKS and ?VS_BLMS, the simulation is carried out on the PC and the performance comparison with the original block processing algorithm NBLMS_S is made. Through the analysis of the performance and the computational complexity, it is found that the improved algorithms have the faster convergence speed and higher convergence accuracy. According to the analysis of the anti-noise property, ?VS_BLMS is more suitable for the application of digital hearing aids microminiaturizing and expands the application range of hearing aids.