Information AboutSpdif |
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S/PDIF or '''S/P-DIF''' stands for ''' Sony / Philips Digital Interface Format''', also ''' IEC 958 type II''', part of IEC-60958. It is a collection of hardware and low-level protocol specifications for carrying PCM Stereo Digital Audio Signal s between Device s and Stereo Component s. S/P-DIF is a consumer version of the standard known as AES/EBU ; it provides small differences in the protocol and requires less expensive hardware. APPLICATIONS S/PDIF is primarily used with CD players (and DVD Player s playing CDs), but has become common on other Audio components like MiniDisc s and modern Computer audio Card s. It is also popular in Car Audio , where a large amount of Wiring can be replaced with a single Fiber Optic Cable , which is immune to Electrical Noise . Another common use for the S/PDIF interface is to carry Compressed digital audio as defined by the standard IEC 61937. This mode is used to connect the output of a DVD player to a home theater receiver that supports Dolby Digital or DTS Surround Sound . HARDWARE SPECIFICATIONS The "S/PDIF" specifications allow several different types of cables and connectors which must match the device being used. Key words for the electrical type are " Coaxial " and " RCA Jack ." The other type is called " Optical " with the word " TOSLINK " often used, or less-often, EIAJ Optical . Adaptors do exist to convert the coaxial RCA Jack S/PDIF to the optical TOSLINK S/PDIF and vice versa (though most individual adaptors are one-way only). All require some sort of external power supply. The "optical" version is suitable for several applications because of its immunity to Electrical Noise . S/PDIF was developed from a standard used in the Professional Audio Field , known as AES/EBU which is commonly used in Digital Audio Tape (DAT) systems and for transmissions in professional studio recording. S/PDIF remained identical at the Protocol level, but changed the physical Connector s from XLR to either electrical coaxial RCA Jack s or optical TOSLINK , both of which cost less and are easier to use. The cable was also changed from 110 Ω ( Ohms ) Impedance Balanced Twisted Pair to the already far more common (and therefore Compatible and inexpensive) 75 Ω Coaxial Cable , using RCA jacks instead of the "F" connector found in Cable Television . S/PDIF is, for all intents, a Consumer Version of the AES/EBU Format . PROTOCOL SPECIFICATIONS 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/P-DIF is meant to be used for transmitting 20 bit audio data streams plus other related information. It can be reduced to 16 bits by renouncing the extra information, or expanded to 24 bits by zero padding. Since the low-level protocol is almost the same, it is described in the AES/EBU article. The only difference is in the "Channel status bit". The channel status bit in the S/P-DIF There is one channel status bit in each subframe, making a 192 bits word each audio block. This means that there are 192/8 = 24 bytes available each audio block. The meaning of the channel status bit is completely different between AES/EBU and the S/P-DIF. For the SPDIF, the 192 bit word is divided in 12 words of 16 bits each. The first 6 bits of the first word are a control code; the meaning of its bits are shown in detail in the following table: OTHER INFORMATION S/PDIF is defined by the international standard IEC 60958-3. S/PDIF is covered by the following Patent : EP000000811295B1. It can be downloaded here: http://depatisnet.dpma.de SEE ALSO EXTERNAL LINKS REFERENCES
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