S/PDIF passthrough is a feature that allows your computer to bundle audio and non-audio data together when sending data to a receiver. For example, an S/PDIF passthrough link can send the information needed to decode an audio stream for multiple surround speakers. Some of the supported data stream types include Windows Media Audio Pro, Dolby Digital and DTS.
About S/PDIF
S/PDIF is a standard developed by Sony and Philips for the transmission of digital audio information over a fiber optic or coaxial cable. When you connect speakers directly to your computer, the sound card or audio chip performs a digital-to-analog conversion before sending sounds to the speaker. Connecting your computer to the receiver digitally allows the receiver to perform the conversion instead. If you have a high-end receiver, this may result in improved audio quality.
Requirements
To use the S/PDIF passthrough feature, your computer must have a sound card or audio chip with an optical or coaxial S/PDIF output. You also must have a stereo or home theater receiver with an S/PDIF input port. If the two ports do not match, you can purchase a coaxial-to-optical converter box. These generally cost under $20. In addition, the receiver must be capable of decoding the data sent over the link.
Connecting
To connect your computer to a receiver via S/PDIF, simply connect one end of an optical or coaxial cable to your computer's digital audio output port and connect the other end to the receiver's input port. If you use a converter box, you need one of each type of cable. If your computer has both types of digital outputs, do not use both simultaneously. You may also need to adjust the settings in the Windows audio mixer to mute the speakers connected directly to your computer and raise the volume of the digital audio output.
Troubleshooting
If you are having difficulty getting your computer's S/PDIF passthrough connection to transmit data to an external receiver, look for a device driver update for your computer's sound card or integrated audio chip. If Windows is using a generic device driver, some hardware-specific features such as S/PDIF passthrough may not work. If you continue to experience a problem, you may need to use the Windows update service to download and install all available updates for your operating system. Some Windows versions such as Windows 98 SE require updates to process S/PDIF passthrough data. Note that versions of Windows older than Windows 98 SE do not support S/PDIF passthrough at all.