Noise reduction for hearing aids using digital signal processing

1. 本文提出了一种降低平稳/非平稳环境噪声的算法，并通过计算机仿真进行了验证。此外，利用信号处理系统构建了全降噪系统。在环境噪声降噪方面，将自适应波束形成技术与传统的固定波束形成器相结合，实现了对静态噪声和非平稳噪声的鲁棒衰减。另一方面，为了减少啸叫，引入了自适应反馈对消器。该系统已应用于实际环境噪音，并在降噪量和其他问题方面进行了评估。结果表明：在环境噪声方面，大功率的方向性噪声降低了20 dB以上，混响等非方向性噪声也降低了10 dB。嚎叫的余量增加了20 dB.3。将降噪系统应用于受噪声干扰的语音，并进行了听力测试。结果表明：在环境降噪方面，引入该系统后，语音可理解度从50%提高到70%。在啸叫消除方面，传统的自适应反馈消除器会破坏语音等周期性信号。然而，在我们的系统中，使用频率压缩器和自适应反馈抵消器产生很少的损坏，并且对语音可理解性没有影响。

1. Algorithm for noise reduction An algorithm for reducing stationary/nonstationary environmental noise has been developed and has been verified via computer simulation. Moreover, total noise reduction system has been constructed using signal processing system. For ebvironmental noise reduction, an adaptive beamforming technique was combined with conventional fixed beamformer to obtain robust attenuation for not only stationary noise but also nonstationary noise. On the other hand, for reducing howling, adaptive feedback canceler was introduced.2. Evaluation The system developed has been applied to real environmental noise and was evaluated in terms of the amount of noise reduction and other issues. The results can be summarized as follows : As for the environmental noise, directional noise with large power was reduced by more than 20 dB,while nondirectional noise such as reverberation is also reduced by 10 dB.As for the howling, howling margin increased by 20 dB.3. Improvement in Speech Intelligibility Noise reduction system has been applied to the speech corrupted by noise, and the listening test was conducted. The results can be summarized as follows : As for the environmental noise reduction, the speech intelligibility was improved from 50 % to 70 % by introducing the proposed system. As for the howling cancellation, periodic signals such as voiced speech is corrupted by the conventional adaptive feedback canceler. However, use of frequency compressor together with adaptive feedback canceler as proposed in our system yields little corruption and no effect on speech intelligibility.