近年來多媒體通訊科技與網際網路發展相當迅速，數位化的視訊及音訊與生活密不可分。人們對於多媒體品質的要求越來越嚴格，也因此傳統單聲道或是雙聲道音訊漸漸地不合人們之需求，所以多聲道音訊存取與播放勢在必行。 本研究中首先介紹改良標準 ITU-R BS.775-1之降混音架構，可將5.1聲道的音訊轉成4個聲道，再行額外加入頭部相關轉移函數與人工迴響器提升距離及空間聽覺感受。當中加入頭部相關轉移函數是希望達到傳統立體聲耳機缺乏的頭部前後聽覺之差異，另一方面加入人工迴響器則是希望提升音訊空間上的聽覺感受。 經過主觀聽覺測試評分後，用提出的四聲道耳機可以達到與多聲道裝置相差不遠之聽覺感受，並且提出的四聲道耳機的硬體成本也比多聲道裝置廉價許多。 With the rapid development of information technology and Internet in recent years, digital video and audio applications are widely used in human life. For the increasing demands of human perception of multimedia, the traditional mono or stereo audio playback is not able to satisfy human ears. Therefore, multi-channel audio systems become more popular. However, in the views of limited available personal space and relatively expensive multi-channel audio system, a low-cost multi-channel audio player, such as a headset, that can be used anytime or anywhere is very attractive. In this work, we design a four-channel headset to achieve the 5.1-channel-like hearing experience. In the proposed architecture, we first modify the down-mixing structure in ITU-R BS.775-1 standard to convert 5.1-channel audio into four channels. Second, we utilize the head related transfer function (HRTF) to enhance the position difference between front and rear, which is missing in traditional stereo earphones. In addition, we utilize artificial reverberation to enhance the hearing experience in a closed space. From subjective hearing tests, the proposed four-channel headset achieves almost the same hearing perception as a 5.1-channel system while the hardware cost of the proposed four-channel headset is much lower than a 5.1-channel system.
