Digital Audio Interfaces
Richard Brice18.1 Digital Audio Interfaces ........................................................................................
Many of the advantages of digital signal processing are lost if signals are repeatedly
converted back and forth between the digital and analogue domain. So that the number of
conversions could be kept to a minimum, as early as the 1970s, manufacturers started to
introduce proprietary digital interface standards enabling various pieces of digital audio
hardware to pass digital audio information directly without recourse to standard analogue
connections. Unfortunately, each manufacturer adopted its own standard, and the Sony
digital interface (SDIF) and the Mitsubishi interface both bear witness to this early epoch
in digital audio technology when compatibility was very poor between different pieces of
equipment. It wasn’t long before customers were demanding an industry-standard interface
so that they could “ mix and match ” equipment from different manufacturers to suit their
own particular requirements. This pressure led to the introduction of widespread, standard
interfaces for the connection of both consumer and professional digital audio equipment.
The requirements for standardizing a digital interface go beyond those for an analogue
interface in that, as well as defi ning the voltage levels and connector style, it is necessary
to defi ne the data format the interface will employ. The two digital audio interface
standards described here are:
(1) The two-channel, serial, balanced, professional interface (the so-called AES/EBU or
IEC958 type 1 interface).
(2) The two-channel, serial, unbalanced, consumer interface (the so-called SPDIF or
IEC958 type 2 interface).
CHAPTER 18