S/PDIF (Sony/Philips Digital Interface)is a type of digital audio interconnect used in consumer audio equipment to output audio over relatively short distances. The signal is transmitted over either a coaxial cable with RCA connectors or a fiber optic cable with TOSLINK connectors. S/PDIF interconnects components in home theaters and other digital high-fidelity systems.
S/PDIF is based on the AES3 interconnect standard.S/PDIF can carry two channels of uncompressed PCM audio or compressed 5.1/7.1 surround sound (such as DTS audio codec); it cannot support lossless surround formats that require greater bandwidth.
S/PDIF is a data link layer protocol as well as a set of physical layer specifications for carrying digital audio signals between devices and components 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 and Philips were the primary designers of S/PDIF. S/PDIF is standardized in IEC 60958 as IEC 60958 type II (IEC 958 before 1998).
A common use for the S/PDIF interface is to carry compressed digital audio for surround sound as defined by the standard IEC 61937. This mode is used to connect the output of a DVD player or computer, via optical or coax, to a home theatre amplifying receiver that supports Dolby Digital or DTS. Another common use is to carry two channels of uncompressed digital audio from a CD player to an amplifying receiver.
S/PDIF was developed at the same time as the main standard, AES3, used to interconnect professional audio equipment in the professional audio field. This resulted from the desire of the various standards committees to have at least sufficient similarities between the two interfaces to allow the use of the same, or very similar, designs for interfacing ICs. Ω balanced twisted pair to 75 Ω coaxial cable, using RCA jacks.S/PDIF remained nearly identical at the protocol level, but changed the physical connectors from XLR to either electrical coaxial cable (with RCA connectors) or optical fibre (TOSLINK; i.e., F05 or EIAJ optical), both of which cost less than the XLR connection. The RCA connectors are typically colour-coded orange to differentiate from other RCA connector uses such as composite video. The cable was also changed from 110
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.
|AES3 balanced||AES3 unbalanced||S/PDIF|
|Cabling||110 Ω STP||75 Ω coaxial||75 Ω coaxial or optical fibre|
|Connector||3-pin XLR||BNC||RCA or TOSLINK|
|Output level||2–7 V peak to peak||1.0–1.2 V peak to peak||0.5–0.6 V peak to peak|
|Min. input level||0.2 V||0.32 V||0.2 V|
|Max. distance||100 m||1000 m||10 m|
|Modulation||Biphase mark code||Biphase mark code||Biphase mark code|
|Subcode information||ASCII id. text||ASCII id. text||SCMS copy protection info.|
|Audio bit depth||24 bits||24 bits||20 bits (24 bits optional)|
S/PDIF is used to transmit digital signals of a number of formats, the most common being the 48 kHz sample rate format (used in DAT) and the 44.1 kHz format, used in CD audio. In order to support both systems, as well as others that might be needed, the format has no defined data rate. Instead, the data is sent using biphase mark code, 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 is identical to AES3 with one exception: the channel status bit differs in S/PDIF. 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. The meaning of the channel status word is completely different between AES3 and S/PDIF. For S/PDIF, the 192-bit status word is identical between the two channels and is divided into 12 words of 16 bits each, with the first 16 bits being a control code.
|Bit||Unset (0)||Set (1)|
|0||Consumer (S/PDIF)||Professional (AES3)|
(changes meaning to AES3 channel status word)
|2||Copy restrict||Copy permit|
|3||2 channels||4 channels|
|6–7||Mode, defines subsequent bytes, always zero|
|8–14||Audio source category (general, CD-DA, DVD, etc.)|
|15||L-bit, original or copy (see text)|
Bits 8–14 of the control code are a 7-bit category code indicating the type of source equipment, and bit 15 is the "L-bit", which (for most category codes) indicates whether copy-restricted audio is original (may be copied once) or a copy (does not allow recording again). The L-bit is only used if bit 2 is zero, meaning copy-restricted audio. The L-bit polarity depends on the category, with recording allowed if it is 1 for DVD-R and DVD-RW, but 0 for CD-R, CD-RW, and DVD. For plain CD-DA (ordinary nonrecordable CDs), the L-bit is not defined, and recording is prevented by alternating bit 2 at a rate of 4–10 Hz.
The receiver does not control the data rate, so it must avoid bit slip 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 used to synchronize reception may produce jitter.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.
TOSLINK optical fiber, unlike coaxial cables, are immune to ground loops and RF interference.The fiber core of TOSLINK, however, may suffer permanent damage if tightly bent.
Digital audio is a representation of sound recorded in, or converted into, digital form. In digital audio, the sound wave of the audio signal is typically encoded as numerical samples in a continuous sequence. For example, in CD audio, samples are taken 44,100 times per second, each with 16-bit sample depth. Digital audio is also the name for the entire technology of sound recording and reproduction using audio signals that have been encoded in digital form. Following significant advances in digital audio technology during the 1970s and 1980s, it gradually replaced analog audio technology in many areas of audio engineering and telecommunications in the 1990s and 2000s.
SCART is a French-originated standard and associated 21-pin connector for connecting audio-visual (AV) equipment. The name SCART comes from Syndicat des Constructeurs d'Appareils Radiorécepteurs et Téléviseurs, "Radio and Television Receiver Manufacturers' Association", the French organisation that created the connector in the mid-1970s. The related European standard EN 50049 has been then refined and published in 1978 by CENELEC, calling it péritelevision, but it is commonly called by the abbreviation péritel in French.
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 and female jack are called RCA plug and RCA jack.
AES3 is a standard for the exchange of digital audio signals between professional audio devices. An AES3 signal can carry two channels of PCM audio over several transmission media including balanced lines, unbalanced lines, and optical fiber.
In telecommunication and data transmission, serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. This is in contrast to parallel communication, where several bits are sent as a whole, on a link with several parallel channels.
The Serial Copy Management System (SCMS) is a copy protection scheme that was created in response to the digital audio tape (DAT) invention, in order to prevent DAT recorders from making second-generation or serial copies. SCMS sets a "copy" bit in all copies, which prevents anyone from making further copies of those first copies. It does not, however, limit the number of first-generation copies made from a master.
Serial digital interface (SDI) is a family of digital video interfaces first standardized by SMPTE in 1989. For example, ITU-R BT.656 and SMPTE 259M define digital video interfaces used for broadcast-grade video. A related standard, known as high-definition serial digital interface (HD-SDI), is standardized in SMPTE 292M; this provides a nominal data rate of 1.485 Gbit/s.
High-Definition Multimedia Interface (HDMI) is a proprietary audio/video interface for transmitting uncompressed video data and compressed or uncompressed digital audio data from an HDMI-compliant source device, such as a display controller, to a compatible computer monitor, video projector, digital television, or digital audio device. HDMI is a digital replacement for analog video standards.
In digital audio electronics, a word clock or wordclock is a clock signal used to synchronise other devices, such as digital audio tape machines and compact disc players, which interconnect via digital audio signals. Word clock is so named because it clocks each audio sample. Samples are represented in data words.
I²S, is an electrical serial bus interface standard used for connecting digital audio devices together. It is used to communicate PCM audio data between integrated circuits in an electronic device. The I²S bus separates clock and serial data signals, resulting in simpler receivers than those required for asynchronous communications systems that need to recover the clock from the data stream. Alternatively I²S is spelled I2S or IIS. Despite the similar name, I²S is unrelated to the bidirectional I²C (IIC) bus.
Dolby Digital Plus, also known as Enhanced AC-3 is a digital audio compression scheme developed by Dolby Labs for transport and storage of multi-channel digital audio. It is a successor to Dolby Digital (AC-3), also developed by Dolby, and has a number of improvements including support for a wider range of data rates, increased channel count and multi-program support, and additional tools (algorithms) for representing compressed data and counteracting artifacts. While Dolby Digital (AC-3) supports up to five full-bandwidth audio channels at a maximum bitrate of 640 kbit/s, E-AC-3 supports up to 15 full-bandwidth audio channels at a maximum bitrate of 6.144 Mbit/s.
Asynchronous Serial Interface, or ASI, is a method of carrying an MPEG Transport Stream (MPEG-TS) over 75-ohm copper coaxial cable or optical fiber. It is popular in the television industry as a means of transporting broadcast programs from the studio to the final transmission equipment before it reaches viewers sitting at home.
An audio/video receiver (AVR) is a consumer electronics component used in a home theater. Its purpose is to receive audio and video signals from a number of sources, and to process them and provide power amplifiers to drive loudspeakers and route the video to displays such as a television, monitor or video projector. Inputs may come from a satellite receiver, radio, DVD players, Blu-ray Disc players, VCRs or video game consoles, among others. The AVR source selection and settings such as volume, are typically set by a remote controller.
Multichannel Audio Digital Interface (MADI) standardized as AES10 by the Audio Engineering Society (AES) defines the data format and electrical characteristics of an interface that carries multiple channels of digital audio. The AES first documented the MADI standard in AES10-1991, and updated it in AES10-2003 and AES10-2008. The MADI standard includes a bit-level description and has features in common with the two-channel AES3 interface.
McASP is an acronym for Multichannel Audio Serial Port, a communication peripheral found in Texas Instruments family of digital signal processors (DSPs) and Microcontroller Units (MCUs).
The McASP functions as a general-purpose audio serial port optimized for the needs of multichannel audio applications. Depending on the implementation, the McASP may be useful for time-division multiplexed (TDM) stream, Inter-Integrated Sound (I2S) protocols, and intercomponent digital audio interface transmission (DIT). However, some implementations are limited to supporting just the Inter-Integrated Sound (I2S) protocol.
The McASP consists of transmit and receive sections that may operate synchronized, or completely independently with separate master clocks, bit clocks, and frame syncs, and using different transmit modes with different bit-stream formats. The McASP module also includes up to 16 serializers that can be individually enabled to either transmit or receive. In addition, all of the McASP pins can be configured as general-purpose input/output (GPIO) pins.
The ADAT Lightpipe, officially the ADAT Optical Interface, is a standard for the transfer of digital audio between equipment. It was originally developed by Alesis but has since become widely accepted, with many third party hardware manufacturers including Lightpipe interfaces on their equipment. The protocol has become so popular that the term "ADAT" is now often used to refer to the transfer standard rather than to the Alesis Digital Audio Tape itself.
An audio signal is a representation of sound, typically using either a changing level of electrical voltage for analog signals, or a series of binary numbers for digital signals. Audio signals have frequencies in the audio frequency range of roughly 20 to 20,000 Hz, which corresponds to the lower and upper limits of human hearing. Audio signals may be synthesized directly, or may originate at a transducer such as a microphone, musical instrument pickup, phonograph cartridge, or tape head. Loudspeakers or headphones convert an electrical audio signal back into sound.
Audio connectors and video connectors are electrical or optical connectors for carrying audio or video signals. Audio interfaces or video interfaces define physical parameters and interpretation of signals. For digital audio and digital video, this can be thought of as defining the physical layer, data link layer, and most or all of the application layer. For analog audio and analog video these functions are all represented in a single signal specification like NTSC or the direct speaker-driving signal of analog audio.
TOSLINK is a standardized optical fiber connector system. Also known generically as optical audio, its most common use is in consumer audio equipment, where it carries a digital audio stream from components such as CD and DVD players, DAT recorders, computers, and modern video game consoles, to an AV receiver that can decode two channels of uncompressed lossless PCM audio or compressed 5.1/7.1 surround sound such as Dolby Digital or DTS Surround System. Unlike HDMI, TOSLINK does not have the bandwidth to carry the lossless versions of Dolby TrueHD, DTS-HD Master Audio, or more than two channels of PCM audio.
IEC 60958 is the International Electrotechnical Commission's standard on digital audio interfaces. It reproduces the AES3 professional digital audio interconnect standard and the consumer version of the same, S/PDIF.
...connections such as S/PDIF do not have the bandwidth necessary to deliver uncompressed surround sound...
The components of a sound card are: [...] An SPDIF digital output (Sony Philips Digital Interface, also known as S/PDIF or S-PDIF or IEC 958 or IEC 60958 since 1998). This is an output line that sends digitised audio data to a digital amplifier using a coaxial cable with RCA connectors at the ends.
|journal=(help) AES Convention 121, paper 6948
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