使用S/PDIF送音频从您的个人计算机
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许多人有什么的一个常规想法 S/PDIF 是 -- 或许通过看见它作为一个标签在音频输出，或者在特点名单为产品。 但它确切地是什么和怎么您使用它？ 这个岗位将包括其中一些细节。
在个人计算机，音频被存放并且被处理数字式地直到最后的产品阶段，当它通常被转换成直接地哺养您的报告人的一个模拟信号时。 然而，也许有时期，当您想要传达信号数字式地给将使用演奏声音时的一个不同的设备，例如接收器。 在这些情况下，您可以想要延期转换信号到一模式一个和改为传送信号数字式地避免也许发生，当传送一个模拟信号时的所有退化和附加噪声。
为此， S/PDIF (索尼或Philips数字式互联格式)被开发了。 经常由连接器的名字提到(包括Toslink、RCA或者简单地“光学”或“数字式”)， S/PDIF指定传送一个数字信号方法，以便它可以由连接的设备正确地接受和解释。 您可以要求自己， “怎样复杂化是传送信号的它？ 为什么我们需要一个特别协议？“考虑数字信号包括一系列的位，并且在那之内系列，位被编组对应于音频样品，并且编组那些的一个更大的子集对应于一种特殊渠道。 为了使接收器适当地解释所有那些位按正确顺序，有一个格式为传送那些位是必要的。 这是S/PDIF来in.的地方。
S/PDIF在真正的时间可以用于传送数字式音频二种渠道在唯一连接。 S/PDIF指定接收器可能使用锁上小河的一个特殊位组合。 一旦接收器有synced与小河， S/PDIF指定音频位的定货，并且怎么在小河应该安排他们，以便接收器可能适当地解释它。
However, there may be times when you wish to transmit more than two channels of audio over the S/PDIF link. This is where compressed audio can be used. Audio compression is a technique used to transmit equivalent information using fewer bits. This is done through a number of techniques. Some techniques, referred to as perceptual coding, take advantage of the fact that humans can only hear certain sounds. These methods of compression usually involve discarding bits that only contribute a minimal amount to what a listener needs to recognize a given sound. Other methods take advantage of numerical redundancies in the signal in order to effectively transmit the same information in a smaller amount of space. Dolby Digital and DTS are two common types of compression. Regardless of the technique, compression enables a digital audio signal to use fewer bits to transmit the audio.
The result of this compression is that it enables you to transmit the content for up to 5.1 channels of audio over S/PDIF in space that would have only fit 2 channels if the audio had been uncompressed. This is great once the signal has been encoded (synonymous with compressed), but once a signal has been encoded, that same signal must also be decoded after it has been received so that it can be sent to speakers. This means that your receiver must be capable of decoding the compressed audio signal in order for you to hear the correct sound. This is the tradeoff necessary to allow you to transmit more than two channels of audio over S/PDIF.
Another direct consequence of transmitting a compressed audio signal instead of an uncompressed audio signal (more commonly known as PCM) is that the volume of that signal cannot be modified once it has been encoded. Because the bits in an encoded signal no longer directly correspond to the volume of that signal, it is impossible to increase the volume until it is decoded. This explains why your PC cannot control the volume of your sound when you are using Dolby Digital or DTS as the output. The connected device will be the only place where the volume can be changed.
To recap, in order to avoid the electrical interference and noise present on an analog connection, consider using S/PDIF to transmit the signal digitally. If you'd like to transmit more than two channels, consider sending encoded content which allows you up to 5.1 channels over S/PDIF. You may also want to consider HDMI, but that's a post for another time!
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