適用於數位助聽器之10毫秒群延遲且近似於ANSI S1.11 1/3-octave規範的濾波器組

Abstract

由於ANSI S1.11 1/3-octave標準中所定義的濾波器組其分頻方式接近人類的聽覺系統，因此適合用在助聽器的應用上，然而因為其群延遲高且運算複雜度大，現今助聽器中的濾波器組大多不採用ANSI S1.11 1/3-octave的規格。有鑑於此，本篇論文提出一近似於ANSI S1.11 1/3-octave濾波器組的設計，藉由對規格作些微的放寬來使群延遲達到10毫秒的規格標準。本篇論文並提出了可以降低和處方之間匹配誤差的方法，使濾波器規格的放寬只會對助聽器受到些微的影響，助聽器和處方之間最大的誤差從0dB上升到了1.5dB，但仍然小於人耳最小感受度範圍限度的3dB。此外本篇論文在其演算法及硬體架構上都進行了最佳化來達到低運算複雜度和低功耗的要求，以適合助聽器的需求。此濾波器組採用了IFIR以及multirate的架構以大幅降低運算量。此濾波器組比起傳統的ANSI S1.11 FIR濾波器組設計只需要其7%運算複雜度以及26%的儲存空間。另外，本論文同時完成了此濾波器組的硬體架構設計並在UMC 90奈米製程下進行實作。根據模擬的結果，此濾波器組在24KHz的取樣頻率下只消耗104μW的功率，比起其他群延遲在10毫秒以下並且針對助聽器應用所設計的濾波器組，本論文所提出的濾波器組在相同的功耗下，可以有更好的處方匹配能力

The ANSI S1.11 1/3-octave filter bank is popular in many acoustic applications because it matches the human hearing characteristics. However, the long group delay and the high computational complexity limit the usage in hearing aids. A Quasi-ANSI S1.11 18-band 1/3-octave filter bank is proposed to reduce the group delay. With the proposed matching error optimization method, the results show that the filter bank achieve comparable good matching between prescriptions and hearing aid response. The maximum matching error is only slight increase from 0dB to 1.5dB. Besides, the group delay is significantly reduced from 78ms to 10ms compared with the ANSI S1.11 1/3-octave filter bank design in [20]. On the other hand, the complexity-effective filter bank architecture is developed by exploiting the interpolated FIR and multirate processing techniques. Results shows that the proposed algorithm saves about 93% of multiplications and 74% of storage elements compared with a straightforward FIR filter bank. The low-delay complexity-effective 1/3-octave filter bank is implemented in UMC 90nm CMOS technology. The design consumes only 104μW, which is lower then other works in the literatures with group delay small then 10ms.