An Overview to SPDIF
Class I-7 by Prof. John McLaughlin
SPDIF stands for Sony/Philips Digital Interconnect Format. This is an audio format used for
carrying digital audio signals on DVD players, CD players, computer sound cards and car
audio systems. The format is also known as IEC 958 type II, S/P-DIF and S/PDIF.
Two 192 bit blocks (right and left channel data) are used. These are segregated into a dozen
16 bit words. The control codes are the initial six bits. This audio format does not provide a
specific resolution or data rate. The apparatus holding the connectors will establish the data
rate hand shake.
Bi-Phase Mark Code and Data Rates
The audio format uses the Bi-phase mark code. This code can have one or two transitions per
bit. This feature permits the first word clock to be pulled out of the base signal. 44.1 kHz and
48 kHz are the most common rates used by the format. 48 kHz is (DAT- Digital Audio Tape)
data rate. 44.1 kHz is for CD audio.
It should be noted that the SPDIF format can support 20 bit audio. However, standard
transmissions are limited to 16 bit audio. The protocol can also support 24 bit audio. This is
not natively supported however. If signals less than 20 bits are to be transmitted, the irrelevant
bits will be trimmed off.
Audio Data Format Information
Data is relayed by 32-bit data word streams. A frame is made up of 384 words. 192 of the
words are used for the stereo A channel. The other 192 words are for the stereo B channel.
The specs of the program are set by the IEC standard 60958-3.
The format is also part of the AES/EBU standards. This is also known as the IEC-60958
standards. Its designation is IEC-958 type II. The digital audio format is actually derivative of
AES/EBU. At the protocol level, the two are very similar.
The connectors were changed from the XLR (commercial and professional audio equipment)
to TOSLINK or RCA. These were adapted because they have proven easier to work with.
This modification meant changing the format’s cable as well. When used with RCA jacks,
one is able to listen to high quality sound previously available in costly commercial
The format has two major purposes. It is used mainly for sending out digital audio according
to the IEC 61937 standard. The second is to relay the signal between the player or computer
to the home theater. This is applicable in home theaters with DTS surround sound) or Dolby
Digital. The SPDIF format is utilized for inter-connecting commercial audio apparatus. Aside
from the technical features specified, the format can also reduce static and noise. This is
possible because the format uses fiber optic cable.