使用S/PDIF送音頻從您的個人計算機
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許多人有什麼的一個常規想法 S/PDIF 是 -- 或許通過看見它作為一個標籤在音頻輸出，或者在特點名單為產品。 但它確切地是什麼和怎麼您使用它？ 這個崗位將包括其中一些細節。
在個人計算機，音頻被存放并且被處理數字式地直到最後的產品階段，當它通常被轉換成直接地哺養您的報告人的一個模擬信號時。 然而，也許有時期，當您想要傳達信號數字式地給將使用演奏聲音時的一個不同的設備，例如接收器。 在這些情況下，您可以想要延期轉換信號到一模式一個和改為傳送信號數字式地避免也許發生，當傳送一個模擬信號時的所有退化和附加噪聲。
為此， S/PDIF (索尼或Philips數字式互聯格式)被開發了。 經常由連接器的名字提到(包括Toslink、RCA或者簡單地「光學」或「數字式」)， S/PDIF指定傳送一個數字信號方法，以便它可以由連接的設備正確地接受和解釋。 您可以要求自己， 「怎樣複雜化是傳送信號的它？ 為什麼我們需要一個特別協議？「考慮數字信號包括一系列的位，并且在那之內系列，位被編組對應於音頻樣品，并且編組那些的一個更大的子集對應於一種特殊渠道。 為了使接收器適當地解釋所有那些位按正確順序，有一個格式為傳送那些位是必要的。 這是S/PDIF來in.的地方。
S/PDIF在真正的時間可以用於傳送數字式音頻二種渠道在唯一連接。 S/PDIF指定接收器可能使用鎖上小河的一個特殊位組合。 一旦接收器有synced與小河， S/PDIF指定音頻位的定貨，并且怎麼在小河應該安排他們，以便接收器可能適當地解釋它。
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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