以DSP實現之主動式耳機開發

DSP based Active Headset Development

張鴻杰(Hong-Jie Chang)

指導教授 ： 蕭俊祥

國立臺北科技大學/機電學院/機電整合研究所/碩士(2006年)

https://doi.org/10.6841/NTUT.2006.00379

摘要

本論文主要目標是開發低價位DSP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的噪音確實會讓人類的身心受到影嚮，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。
實驗方法首先我們將市售簡單的小型電容式麥克風自行設置於耳機內，由於麥克風的輸出壓訊號過於微弱，故我們透過簡易的訊號放大電路來放大麥克風的電壓輸出。音樂訊號則透過IIR數位濾波器模擬音樂訊號的輸出，並搭配Filtered-X LMS演算法作為控制器更新律，使用整合型回授主動式噪音控制架構進行外部噪音之減噪。
在以低價位DSP實現控制器ANC部份，實驗結果顯示，應用主動控制於外部單頻噪音訊號，FXLMS演算法有平均約15dB的減噪量，對於複頻噪音訊號則有平均約20dB的減噪量，而對於雙頻交替噪音訊號則有平均約10dB的減噪量。由此可驗證，以低價位DSP實現之主動式噪音控制在抑制低頻有良好的效果。

關鍵字

主動式耳機 ； Filtered-X LMS演算法 ； 數位訊號處理器 ； 整合型回授主動式噪音控制

並列摘要

The purpose of this thesis is to develop an active noise control (ANC) earphones with low cost DSP chip such that background noise can be cancelled while listening to the music. Moreover, active headsets can also be used by workers who have to work under the environment with louder noise for long working hour. According to many literatures, louder noise is certainly affecting the human’s health; hence, we would like to use active headset to prevent the injury of human ear, caused by exposing to noise.
In the experimental setup, we firstly placed microphones of capacitor type into the earphones. However, the output signals of microphones are too weak to be used. Therefore, we employed amplifiers for the output voltages of microphones. The output of music signal from player is simulated by an IIR digital filter; moreover, the Filtered-X LMS algorithm is applied here to tune the controller for rejecting background noises.
In the experiment results, we show that applying ANC for single-frequency noise case can obtain an average of 15 dB noise attenuation; in case of the two-frequency noise, 20 dB noise reduction was observed; and for siren noise with alternating frequencies, 10 dB noise decreasing was achieved. Hence we may conclude that employing ANC with a low-cost DSP is a good approach for rejecting low-frequency noise.

並列關鍵字

Active Headset ； Filtered-X LMS Algorithm ； Digital Signal Processor ； Integrated Feedback Active Noise Control

參考文獻

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