What is S/PDIF?
SPDIF, or S/PDIF, stands for Sony/Philips Digital Interface. It is a technology for transmitting audio data in a digital medium to preserve quality.
In addition to sound cards, there are many consumer electronics devices that feature SPDIF. Examples are DVD players, DVR, HDTV, mini-disc players or recorders, and other devices. By providing SPDIF functionality, these devices can send out, play back, or record audio with zero signal loss. S/PDIF comes in two technologies, Coaxial and Optical.


Which is Better Optical or Coax?
Quite simply nobody really knows. It is a widely disputed topic on the web and electronics comunity. Really when it comes down to it your ears can't tell.

Coax offers a direct metal to metal connection, faster transfer rate, cheaper cables, and no DAC. Coax however can pick up interference from other devices and can cause noise if not grounded properly.

Optical offers a high quality sound connection with no interference from other devices. Optical however is more expensive, cables can pop out, and greater chance of signal loss.

It comes down to this. Pick what works best for you and your equipment. Some equipment except Coax only or Optical only and some have both.

Optical Connection:
The optical connection for S/PDIF uses fiber optic wire to transmit full digital Audio signal. Through light the binary code, 1's and 0's, are transmitted to the digital device.

Coaxial Connection:
The Coax connection for S/PDIF uses standard metal wire that transmits electrical pulses that are converted into 1's and 0's by the Audio Device.

How would you use it?
For example, your mini-disc player has an SPDIF output and your sound card has an SPDIF input. You could send the output of the mini-disc player to your sound card, then record the incoming audio data as a .WAV file. There would be no noise introduced because it would be a digital signal sent, not analog. Analog signals can tend to pick up noise. Digital signals are normally pure.

Another example is your sound card has an SPDIF out and you have a Dolby Digital receiver. Your computer has a DVD drive, so you can send the AC-3 audio from a DVD movie to the Dolby Digital receiver for decoding.

Also most DVR and Cable Box Tops have S/PDIF coax and optical outputs which can then connect to your receiver to decode the audio. HDMI connectors carry both digital video and audio. When availabe run HDMI to TV for video and sound, then run S/PDIF to receiver for Surround sound.

Reminder: Most high-end HDTV's have S/PDIF optical out on the TV. Therefore you can run HDMI from your device to your TV. Then S/PDIF optical out to your Dolby Receiver.