以數位訊號處理器實現之主動式耳機開發

Development of DSP-Based Active Headset

蕭俊祥(Jin-Siang Shaw) ； 盧士一(Shih-Yi Lu)

《勞工安全衛生研究季刊》 15卷4期 (2007/12) Pp. 362-368

https://doi.org/10.7005/JOSH.200712.0362

摘要

本論文目標是開發低價位數位訊號處理器實現之主動式耳機，希望使用耳機聽音樂時，能夠消除外在背景噪音，使得使用者能夠聽到清晰的音樂。同時主動式耳機也可以應用在長期需要處在高分貝環境工作之工作者，根據許多報告指出高分貝噪音確實會讓人的身心受到影響，所以我們希望能透過主動式耳機降低噪音對於人耳的受傷。
實驗方法首先將市售的小型電容式麥克風安置於耳機內，由於麥克風的輸出電壓訊號過於微弱，因此需透過訊號放大電路來放大麥克風的電壓輸出。本文使用整合型回授主動式噪音控制架構進行耳機外部噪音之減噪，音樂訊號則透過無限脈衝響應(Infinite Impulse Response, IIR)數位濾波器之模擬而分離出來，並搭配Filtered-X Least Mean Square (FXLMS)演算法作爲控制器參數之更新律。實驗結果顯示，應用主動控制於外部單頻噪音訊號，平均有15dB的減噪量；對於複頻噪音訊號則有平均約20dB的減噪量；對於雙頻交替噪音訊號則有約10dB的減噪量。由此可驗證，以低價位DSP實現之主動式耳機在抑制低頻噪音有良好的效果。

關鍵字

數位訊號處理器 ； 主動式耳機 ； 整合型回授主動式噪音控制

並列摘要

The purpose of this paper is to develop active noise control (ANC) earphones using a low cost digital signal processor (DSP). These active headsets are designed to cancel background noise while listening to music, but they can also be used by workers who are exposed to loud noise for extended periods of time.
We would like to use active headsets to prevent injury to the human hearing, specifically that caused by lengthy exposure to loud noise. We started by placing capacitor microphones into the headset. Since the signal from the microphones was too weak, amplifiers were used to amplify the output voltages. An Integrated feedback ANC was employed to attenuate noise outside the earphone. The Music from the CD player was simulated by an infinite impulse response (IIR) digital filter, and the Filtered-X LMS (FXLMS) algorithm was used to reject background noise. Applying the integrated feedback ANC for single-frequency noise case yielded an average 15 dB of noise attenuation; in case of two-frequency noise, a 20 dB noise reduction was observed; and for sirens with alternating frequencies, a 10 dB noise reduction was achieved. Thus, employing integrated feedback ANC with a low-cost DSP is a good approach for rejecting low-frequency noise.

並列關鍵字

Digital signal processor ； Active headset ； Integrated feedback ANC

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