S/PDIF (Sony/Philips Digital Interface) is a type of digital audio interface used in consumer audio equipment to output audio over relatively short distances. The signal is transmitted over either a

coaxial cable Coaxial cable, or coax (pronounced ) is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric ( insulating material); many coaxial cables also have a p ...

(using

RCA The RCA Corporation was a major American electronics company, which was founded as the Radio Corporation of America in 1919. It was initially a patent trust owned by General Electric (GE), Westinghouse, AT&T Corporation and United Fruit Comp ...

or BNC connectors) or a

fiber optic cable A fiber-optic cable, also known as an optical-fiber cable, is an assembly similar to an electrical cable, but containing one or more optical fibers that are used to carry light. The optical fiber elements are typically individually coated with ...

with TOSLINK connectors. S/PDIF interconnects components in home theaters and other digital high-fidelity systems. S/PDIF is based on the

AES3 AES3 is a standard for the exchange of digital audio signals between professional audio devices. An AES3 signal can carry two channels of pulse-code-modulated digital audio over several transmission media including balanced lines, unbalanced ...

interconnect standard. S/PDIF can carry two channels of uncompressed

PCM audio Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the amp ...

or compressed 5.1

surround sound Surround sound is a technique for enriching the fidelity and depth of sound reproduction by using multiple audio channels from speakers that surround the listener (surround channels). Its first application was in movie theaters. Prior to s ...

(such as DTS audio codec or Dolby Digital codec); it cannot support lossless surround formats that require greater bandwidth. S/PDIF is a

data link layer The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer p ...

protocol as well as a set of

physical layer In the seven-layer OSI model of computer networking, the physical layer or layer 1 is the first and lowest layer; The layer most closely associated with the physical connection between devices. This layer may be implemented by a PHY chip. The ...

specifications for carrying digital audio signals over either optical or electrical cable. The name stands for Sony/Philips Digital Interconnect Format but is also known as Sony/Philips Digital Interface.

Sony , commonly stylized as SONY, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. As a major technology company, it operates as one of the world's largest manufacturers of consumer and professional ...

and

Philips Koninklijke Philips N.V. (), commonly shortened to Philips, is a Dutch multinational conglomerate corporation that was founded in Eindhoven in 1891. Since 1997, it has been mostly headquartered in Amsterdam, though the Benelux headquarters is ...

were the primary designers of S/PDIF. S/PDIF is standardized in

IEC The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...

60958 as IEC 60958 type II (IEC 958 before 1998).

Applications

A common use is to carry two channels of uncompressed digital audio from a CD player to an amplifying receiver. The S/PDIF interface is also used to carry compressed digital audio for

as defined by the IEC 61937 standard. This mode is used to connect the output of a

Blu-ray The Blu-ray Disc (BD), often known simply as Blu-ray, is a digital optical disc data storage format. It was invented and developed in 2005 and released on June 20, 2006 worldwide. It is designed to supersede the DVD format, and capable of st ...

DVD player A DVD player is a device that plays DVDs produced under both the DVD-Video and DVD-Audio technical standards, two different and incompatible standards. Some DVD players will also play audio CDs. DVD players are connected to a television to ...

or computer, via optical or coax, to a

home theatre Home cinema, also called home theaters or theater rooms, are home entertainment audio-visual systems that seek to reproduce a movie theater experience and mood using consumer electronics-grade video and audio equipment that is set up in a room ...

amplifying receiver that supports

Dolby Digital Dolby Digital, originally synonymous with Dolby AC-3, is the name for what has now become a family of audio compression technologies developed by Dolby Laboratories. Formerly named Dolby Stereo Digital until 1995, the audio compression is loss ...

or DTS decoding.

Hardware specifications

S/PDIF was developed at the same time as the main standard, AES3, used to interconnect professional audio equipment in the

professional audio Professional audio, abbreviated as pro audio, refers to both an activity and a category of high quality, studio-grade audio equipment. Typically it encompasses sound recording, sound reinforcement system setup and audio mixing, and studio mu ...

field. This resulted from the desire of the various stakeholders to have at least sufficient similarities between the two interfaces to allow the use of the same, or very similar, designs for interfacing ICs. S/PDIF is nearly identical at the

protocol Protocol may refer to: Sociology and politics * Protocol (politics), a formal agreement between nation states * Protocol (diplomacy), the etiquette of diplomacy and affairs of state * Etiquette, a code of personal behavior Science and technology ...

level, but uses either

(with

RCA connector The RCA connector is a type of electrical connector commonly used to carry audio and video signals. The name ''RCA'' derives from the company Radio Corporation of America, which introduced the design in the 1930s. The connectors male plug a ...

s) or

optical fibre An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means t ...

( TOSLINK; i.e., F05 or EIAJ optical), both of which cost less than the XLR connection used by AES3. The RCA connectors are typically colour-coded orange to differentiate from other RCA connector uses such as

composite video Composite video is an analog video signal format that carries standard-definition video (typically at 525 lines or 625 lines) as a single channel. Video information is encoded on one channel, unlike the higher-quality S-Video (two channe ...

. S/PDIF uses 75 Ω coaxial cable while AES3 uses 110 Ω balanced

twisted pair Twisted pair cabling is a type of wiring used for communications in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility. Compared to a single conductor or an untwisted b ...

. Signals transmitted over consumer-grade TOSLINK connections are identical in content to those transmitted over coaxial connectors, though TOSLINK S/PDIF commonly exhibits higher

jitter In electronics and telecommunications, jitter is the deviation from true periodicity of a presumably periodic signal, often in relation to a reference clock signal. In clock recovery applications it is called timing jitter. Jitter is a signific ...

Protocol specifications

S/PDIF is used to transmit digital signals in a number of formats, the most common being the 48 kHz

sample rate In signal processing, sampling is the reduction of a continuous-time signal to a discrete-time signal. A common example is the conversion of a sound wave to a sequence of "samples". A sample is a value of the signal at a point in time and/or spa ...

format (used in Digital Audio Tape) and the 44.1 kHz format, used in

CD audio Compact Disc Digital Audio (CDDA or CD-DA), also known as Digital Audio Compact Disc or simply as Audio CD, is the standard format for audio compact discs. The standard is defined in the ''Red Book'', one of a series of Rainbow Books (named f ...

. In order to support both systems, as well as others that might be needed, the format has no defined

bit rate In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction ...

. Instead, the data is sent using

biphase mark code Differential Manchester encoding (DM) is a line code in digital frequency modulation in which data and clock signals are combined to form a single two-level self-synchronizing data stream. In various specific applications, this method is also call ...

, which has either one or two transitions for every bit, allowing the original word clock to be extracted from the signal itself. S/PDIF is meant to be used for transmitting 20-bit audio data streams plus other related information. To transmit sources with less than 20 bits of sample accuracy, the superfluous bits will be set to zero. S/PDIF can also transport 24-bit samples by way of four extra bits; however, not all equipment supports this, and these extra bits may be ignored. S/PDIF protocol differs

only in the channel status bits. Both protocols group 192 samples into an audio block, and transmit one channel status bit per sample, providing one 192-bit ''channel status word'' per channel per audio block. For S/PDIF, the 192-bit status word is identical between the two channels and is divided into 12

words A word is a basic element of language that carries an objective or practical meaning, can be used on its own, and is uninterruptible. Despite the fact that language speakers often have an intuitive grasp of what a word is, there is no conse ...

of 16 bits each, with the first 16 bits being a control code.

Limitations

The receiver does not control the data rate, so it must avoid

bit slip In digital transmission, bit slip is the loss or gain of a bit or bits, caused by clock drift – variations in the respective clock rates of the transmitting and receiving devices. One cause of bit slippage is overflow of a receive buffer that ...

by synchronizing its reception with the source clock. Many S/PDIF implementations cannot fully decouple the final signal from influence of the source or the interconnect. Specifically, the process of

clock recovery In serial communication of digital data, clock recovery is the process of extracting timing information from a serial data stream itself, allowing the timing of the data in the stream to be accurately determined without separate clock information. ...

used to synchronize reception may produce

.Giorgio Pozzoli.
DIGITabilis: crash course on digital audio interfaces
tnt-audio.com.Chris Dunn, Malcolm J. Hawksford.
Is the AES/EBU/SPDIF Digital Audio Interface Flawed?
AES Convention 93, paper 3360. If the DAC does not have a stable clock reference then noise will be introduced into the resulting analog signal. However, receivers can implement various strategies that limit this influence. AES Convention 121, paper 6948

Notes

References

External links

S/PDIF at Epanorama.net
*

{{DEFAULTSORT:S PDIF Computer hardware standards IEC 60958 Digital audio transport Digital audio connectors