5.1 Surround
5.1环绕/Wu3 Dian3 Yi1 Huan2 Rao4
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5.1环绕声系统是在立体声基础上发展起来的空间感处理系统，主要应用于电影和视频图像的播放。5.1环绕声系统不仅能提供清晰的对话，而且能够提供立体声音乐、效果声和听音环境感，典型的扬声器布置中，除了传统的两个前置扬声器外，还增加了下述的其它扬声器，以满足更高的声音重放要求：
中置对话扬声器：影片对话内容一般由中置扬声器重放，因为实践证明这样可以获得比两声道重放更好的语言清晰度。有趣的是，听觉并不能察觉到语言重放是单声道的。这是因为在声音定位时，视觉起较为重要的作用，因此，听觉总能感到声音来自屏幕上说话人的方向。
环绕声扬声器：环境声和效果声是由后置的环绕声扬声器提供的。由于它们不是用来产生声音的方向感，因此馈送给环绕声场的声音的相关性应尽量小，与前置扬声器信号的相关性也要尽量小，从而使听觉产生声音不是来自特定方向而是来自四面八方的感觉。
低频效果扬声器：在电影和视频节目中，经常会出现如爆炸声、撞击声等声音效果，这些声音包含丰富的低频成分甚至是次声波成分，因此，增加一只低频扬声器是非常必要的。一个专门用于重放低频的扬声器可以满足重放这些效果声的需要。值得注意的是，尽管低音效果扬声器也存在于许多重放音乐的环绕声系统中，但是它们从来不是用来重放音乐信号的。
源自《音乐声学与心理声学》（第三版）、霍华德、安格斯、人民邮电出版社、2011。
5.1 surround systems are used in film and video presentations. Here the objective is to provide both clear dialog and stereo music and sound effects, as well as a sense of ambience. Here, in addition to the conventional stereo speakers there are some additional ones to provide the additional requirements. These are as follows:
Center dialog speaker: The dialog is replayed via a central speaker because this has been found to give better speech intelligibility over a stereo presentation. Interestingly the fact that the speech is not in stereo is not noticeable because the visual cue dominates so that we hear the sound coming from the person speaking on the screen even if their sound is coming from a different direction.
Surround speakers: The ambient sounds, and sound effects, are diffused via rear mounted speakers. However they are, in the main, not supposed to provide directional effects and so are often deliberately designed, and fed signals, to minimize their correlation with each other and the front speakers. The effect of this is to fool the hearing system into perceiving the sound as all around with no specific direction.
Low-frequency effects: This is required because many of the sound effects used in film and video, such as explosions and punches, have substantial low-frequency and subsonic content. Thus, a specialized speaker is needed to reproduce these sounds properly. Note: this speaker was never intended to reproduce music signals, notwithstanding their presence in many surround music systems.
(Source: David M. Howard and Jamie Angus, Acoustics And Psychoacoustics Third Edition. Elsevier 2006)
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