Many users and technicians must have already noticed that CD and DVD drives have an output called SPDIF and many sound cards, especially the more expensive sort, also have a connector labelled SPDIF. But what is it?

Figure 1: CD-ROM Drive SPDIF Output (two pins on the left).

SPDIF stands for Sony/Philips Digital Interface. It is a standard for digitally transferring audio. Digital transference, as opposed to analogue transmission, is immune to noise and according is the kind of transmission loved by audiophiles, musicians and professional people in the audio field that use computers as a tool. In many cases, however, the computer provides a SPDIF connection capability, unused due to unfamiliarity of user's or technician that assembled the computer.

It goes like this: when an audio CD is inserted in a CD-ROM drive, this drive has to convert data, read in digital format, into an analogue audio signal, seeing that sound is an analogue signal. This analogue signal is then sent to the sound card via a suitable cable. For people that care for the signal's noise level, there are two points here that can lower the quality of audio. In the first place, the CD-ROM drive can use a poor quality D/A (digital-analogue) converter and so generate noise. In second place, seeing that transmission between the CD-ROM drive and the sound card is carried out in analogue format, the cable used for connecting may pick up noise from electromagnetic interference inside the computer.

Therefore, if your sound card has a SPDIF input and your CD-ROM drive has a SPDIF output, instead of using the analogue connection you should opt for a SPDIF connection. This connection allows the A/D conversion to take place in the sound card and not in the CD-ROM drive. The connection is set up via two wires and a small two-terminal plug. This cable is easy to make or can be bought ready-made in specialized outlets.

Figure 2 shows in detail a Sound Blaster Live! Sound card. We can see on its upper part the two-pin SPDIF connector for SPDIF-linking the CD-ROM drive and under it the SPDIF EXT connector for connecting external digital sources to the computer over a SPDIF connection.

Figure 2: Detail of a Sound Card Type Sound Blaster Live!

Some motherboards with on-board audio also have a SPDIF input for connecting the CD-ROM, as you can see in Figures 3 and 4. This connector can also be used to plug in an adaptor to put SPDIF external connectors on your PC. We'll talk about this in following pages.

Figure 3: Detail of a Motherboard with on-board audio with a SPDIF Connector.

Figure 4: Another example of a Motherboard with on-board audio with SPDIF Connector.