Digital Sound & Music: Concepts, Applications, & Science, Chapter 5, last updated 6/25/2013
compatible with the equipment you already have. In order to succeed at this, you’ll need to
understand and be able to identify the various options for digital audio transmission.
The most common transmission protocol, particularly in consumer-grade equipment is
the Sony/Phillips Digital Interconnect Format (S/PDIF). With S/PDIF you can transmit two
channels on a single wire. Typically this means you can transmit both the left and right channels
of a stereo pair using a single cable instead of two cables required for analog transmission.
S/PDIF can be transmitted electrically or optically. Electrical transmission involves RCA (Radio
Corporation of America) connectors and a low loss, high bandwidth coaxial cable. This cable is
different from the cable you would use for analog transmission. For S/PDIF you need a cable
like what is used for video. S/PDIF transmits the digital data electrically in a stream of square
wave pulses. Using cheap, low bandwidth cable can result in a loss of high frequency content
that can ultimately lose the square wave form, resulting in data loss. When looking for a cable
for electrical S/PDIF transmission, look for something with RCA connectors on each end and an
impedance of 75 .
S/PDIF can also be transmitted optically using an optical cable with TOSLINK
(TOShiba-LINK) connectors. Optical transmission has the advantage of being able to run longer
distances without the risk of signal loss, and it is not susceptible to electromagnetic interference
like an electrical signal. Optical cables are more easily broken so if you plan to move your
equipment around, you should invest in an optical cable that has good insulation.
Figure 5.18 - S/PDIF connections using RCA and TOSLINK connections
S/PDIF is considered a consumer grade transmission protocol. S/PDIF has a professional
grade cousin called AES3, more commonly known as AES/EBU (Audio Engineering
Society/European Broadcasting Union). The actual format of the digital stream is almost
identical. The main differences are the type of cable and connectors used and the maximum
distance you can reliably transmit the signal. AES/EBU can be run electrically as a balanced
signal using three pin XLR connectors with a 110 twisted pair cable or unbalanced using BNC
connectors a with a 75 coaxial cable. The unbalanced version has a maximum transmission
distance of 1000 meters as opposed to the 100 meters maximum for the balanced version. The
balanced signal is by far the most common implementation as shown in Figure 5.19.