A Novel Subband Fractional Delay Algorithm Based on the Filterbank of Cochlear Implant

Background: In recent years, microphone array method is gradually applied to speech enhancement of cochlear implant, and the delay parameter is the main parameter of microphone array beamforming technology. Due to the size limitation of cochlear implant, the microphone spacing is very small. In algorithm implementation, delay parameter usually corresponds to fractional sampling point. It is necessary to use fractional delay filter to realize the interpolation of integer sampling points. The traditional fractional delay method is to interpolate sampling points in the whole frequency band of speech. However, the speech frequency band itself is very wide, so the error of the present fractional delay method in cochlear is still large. Methods: We propose a fractional delay algorithm based on the filter bank of cochlear implant. The algorithm deduces and calculates the mathematical expression of the fractional delay filter of each subband, and forms a full band fractional delay filter algorithm to minimize the delay error of the whole band. Realization and results: Through the analysis of the system response curve and the calculation of the delay error, it can be seen that the system response corresponding to the fractional delay of each subband in the cochlear filter bank has only a small deviation from the ideal fractional delay filter. Therefore, the error of the fractional delay filter designed in this paper is very small, which can meet the requirements of cochlear implant using microphone array technology for the precision of delay parameters. Discussions: In this paper, the implementation algorithm of subband fractional delay filter is applied to signal acquisition of cochlear implant. Considering the space condition and delay parameters in the actual application scenario, the value of fractional delay can be any continuous real number between 0 and 3, and the error situation of the algorithm can be calculated and analyzed in this range. If the algorithm is extended to other applications, the numerical range of fractional delay can be extended. From the statistics of the average error, it can be seen that the average error of the proposed algorithm in the whole frequency band is extremely small, which can meet the needs of the accuracy of the delay parameters in the application of cochlear implant. Conclusions: The proposed fractional delay filter based on the minimum subband error of cochlear implant can not only realize the local fractional delay minimization, but also the error minimization of the whole frequency band.

Design of Variable Fractional Delay Filter using FIR Filter Approximation

Beamforming plays an important role in the field of wireless communication. Beamforming means combination of a radio frequency (RF) signals from multiple antennas to form a single direction beam. This technique improves the quality of communication and reduces the interference of signal. In beam forming technique, different phases signals can be achieved with different signals and the received phase delay signals are converted into same phase, multiply with weight factor and combined this signals to form a beam in desired direction. The required phase delays are generated by using a Variable fractional delay filter. Variable fractional delay filter is design by using a direct form of a FIR filter structure. Variable fractional delay filter is calculated by two different phase signals from digital antennas and those two different phase signals are converted to in- phase and added together to form a beam forming. As the order of the filter increases, the delay also increases. The filter coefficients of the variable fractional delay filter are calculated my using a Lagrange interpolation method. The variable fractional delay filter is designed by using software Xilinx version 14.3