S/PDIF (Sony/Philips Digital Interface)[1][2] is a type ofdigital audio interface used in consumer audio equipment to output audio over relatively short distances. The signal is transmitted over either acoaxial cable usingRCA orBNC connectors, or afibre-optic cable usingTOSLINK connectors. S/PDIF interconnects components inhome theaters and other digitalhigh-fidelity systems.
S/PDIF is based on theAES3 interconnectstandard.[3] S/PDIF can carry two channels of uncompressedPCM audio orcompressed5.1 surround sound; it cannot support lossless surround formats that require greaterbandwidth.[4]
S/PDIF is adata link layer protocol as well as a set ofphysical layer 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 andPhilips were the primary designers of S/PDIF. S/PDIF is standardized inIEC 60958 as IEC 60958 type II (IEC 958 before 1998).[5]
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 carrycompressed digital audio forsurround sound as defined by theIEC 61937 standard. This mode is used to connect the output of aBlu-ray,DVD player or computer, via optical or coax, to ahome theatre amplifying receiver that supportsDolby Digital orDTS Digital Surround decoding.
.jpg)
S/PDIF was developed at the same time as the main standard, AES3, used to interconnect professional audio equipment in theprofessional audio 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 interfacingICs.[6] S/PDIF is nearly identical at theprotocol level,[a] but uses eithercoaxial cable (withRCA connectors) oroptical fibre (TOSLINK; i.e., JIS F05 or EIAJ optical), both of which cost less than theXLR connection used by AES3. The RCA connectors are typically colour-coded orange to differentiate from other RCA connector uses such ascomposite video. S/PDIF uses 75 Ω coaxial cable while AES3 uses 110 Ωbalancedtwisted pair.
Signals transmitted over consumer-grade TOSLINK connections are identical in content to those transmitted over coaxial connectors. Optical provides electrical isolation that can help addressground loop issues in systems. The electrical connection can be more robust and supports longer connections.[7]
| AES3 | S/PDIF | |||
|---|---|---|---|---|
| Balanced | Unbalanced | Copper | Optical | |
| Cabling | 110 Ω STP | 75 Ω coaxial | 75 Ω coaxial | Optical fibre |
| Connector | 3-pinXLR | BNC | RCA orBNC | 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 | 1000 m | 100 m | 10 m | |
| Modulation | Biphase mark code | |||
| Subcode information | ASCII id. text | SCMS copy protection info. | ||
| Audio bit depth | 24 bits | 20 bits (24 bits, optionally)[citation needed] | ||
S/PDIF is used to transmit digital signals in a number of formats, the most common being the 48 kHzsample rate format (used inDigital Audio Tape andDVDs) and the 44.1 kHz format, used inCD audio. In order to support both sample rates, as well as others that might be needed, the format has no definedbit rate. Instead, the data is sent usingbiphase mark code, which has either one or two transitions for every bit, allowing the originalword clock to be extracted from the signal itself.
S/PDIF protocol differs fromAES3 only in the channel status bits; seeAES3 § Protocol for the high-level view. Both protocols group 192 samples into an audio block, and transmit one channel status bit per sample, providing one 192-bitchannel 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 12words of 16 bits each, with the first 16 bits being a control code.
| Byte | Bit | Unset (0) | Set (1) |
|---|---|---|---|
| 0 | 0 | Consumer (S/PDIF) | Professional (AES3) (changes meaning toAES3 channel status word) |
| 1 | Normal PCM | Compressed data | |
| 2 | Copy restrict | Copy permit | |
| 3 | 2 channels | 4 channels | |
| 4 | — | — | |
| 5 | No pre-emphasis | Pre-emphasis 50/15 | |
| 6–7 | Mode, defines subsequent bytes; values other than zero are undefined. | ||
| 1 | 0–6 | Audio source category indicating the type of source equipment (general, CD-DA, DVD, etc.) | |
| 7 | L-bit, original or copy[A] | ||
| 2 | 0–3 | Source number | |
| 4–7 | Channel number | ||
| 3 | 0–3 | Sampling frequency:00002: 44.1 kHz,01002: 48 kHz,11002: 32 kHz | |
| 4–5 | Clock accuracy:102: 50ppm,002: 1100ppm,012: variable pitch (requires compatible receiver) | ||
| 6–7 | Undefined | ||
| 4 | 0 | Word length 20 bits | Word length 24 bits |
| 1–3 | Sample length (0: undefined, 1–4: word length minus 1-4 bits, 5: full word length) | ||
| 4–7 | Undefined | ||
| 5–10 | 0-7 | EAN-13 code (possibly in binary-coded decimal) | |
| 11 | 0-3 | ||
| 4–7 | Undefined; padding on 13-digit EAN code | ||
| 12–13 | 0-7 | Undefined | |
| 14 | 0–3 | ||
| 4-7 | ISRC (encoding unclear; ISRC is 2 alphabetic, 3 alphanumeric and 7 numeric, which is 262 × 363 × 107 ≈ 248.164 and so obviously fits into 7.5 bytes, but a naive 5 ASCII + 7 BCD would be 8.5 bytes) | ||
| 15–21 | 0–7 | ||
| 22–23 | 0–7 | Undefined | |
S/PDIF block contains 192 frames, and each frame contains two sub-frames. A sub-frame has either 20- or 24-bit audio data.[10]
S/PDIF is meant to be used for transmitting 20-bit audio data streams plus other related information. 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.
To transmit sources with less than 20 bits of sample accuracy, the superfluous bits will be set to zero, and the 4:1–3 bits (sample length) are set accordingly.
IEC 61937 defines a way to transmit compressed, multi-channel data over S/PDIF.[11]
A number of encodings are available over IEC 61937, including DolbyAC-3/E-AC-3,Dolby TrueHD, MP3, AAC,ATRAC,DTS, andWMA Pro.[12][13]
The receiver does not control the data rate, so it must avoidbit 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 ofclock recovery used to synchronize reception may producejitter.[14][15][16] If theDAC 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.[16][17]
...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.
{{cite web}}: CS1 maint: bot: original URL status unknown (link){{cite journal}}:Cite journal requires|journal= (help) AES Convention 121, paper 6948
| General | |
|---|---|
| Standards |
|
| Storage |
|
| Peripheral | |
| Audio | |
| Portable | |
| Embedded | |
Interfaces are listed by their speed in the (roughly) ascending order, so the interface at the end of each section should be the fastest.  Category | |