Sony / Philips digital interface
Sony / Philips Digital Interface ( S / PDIF ) is a specification for a uni-directional , self-synchronizing and serial interface for electrical or optical transmission of digital stereo - or multi-channel - the audio signals between various devices for use in the field of consumer electronics .
S / PDIF is e.g. As in CD -Spielern, DAT recorders, with MiniDisc , between DVD players and home theater - receiver and digital audio cards in PCs used. It is also used in audio systems in vehicles, where an entire cable harness can be replaced by a single fiber optic cable , which is also insensitive to interference . There are also redundant terms: Sony / Philips Digiconnect format, S / PDIF and also TOSLINK (the latter is only used for the optical variant).
Plug connections
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DIN EN 60958 |
|---|---|
| Area | Digital technology |
| title | Digital Audio Interface - Part 1: General, Part 3: General Use, Part 4: Professional Use |
| Latest edition | 2009-03, 2010-09, 2008-09 |
| ISO | IEC 60958 |
S / PDIF is defined in IEC 60958 (formerly IEC 958: 1989 ). In Germany, this standard is published in three parts as DIN EN 60958 .
The standard differentiates between a professional (professional mode, Type I) and an end-user mode (consumer mode, Type II) . The end-user type is used in home hi-fi devices.
A cinch connection with a coaxial cable or, more rarely, a 3.5 mm jack plug (tip: output, ring: input, jacket: GND ) is used as a connector for electrical connections and a TOSLINK connection for optical signal transmission . Some notebooks have jack connections with a combined socket for analog signals and optical TOSLINK.
An adapter with its own power supply is required for the electrical / optical conversion .
The S / PDIF interface is closely related to the AES standard AES-3 , which is primarily used in professional studios and is also known colloquially as AES / EBU. The main differences are the different physical interfaces and the so-called channel status ("C-Bit") of AES-3, which is used in S / PDIF to transmit copy protection data. The remaining data fields, especially the format of the audio data, the structure of frames and subframes, are identical between S / PDIF and AES-3.
Physical interface
The physical interface in S / PDIF is defined as an asymmetrical connection with a voltage of approximately ± 0.5 volts with a characteristic impedance of 75 ohms . It is often referred to as coaxial and uses cinch . In contrast to this, the AES-3 interface has a symmetrical connection according to the EIA-422 (RS-422) standard with 110 ohm characteristic impedance and a voltage of approx. ± 5 volts. XLR connectors are mostly used for AES / EBU . Twisted pair cables are also increasingly being used, mostly in the Cat5 category and higher. The interface is unidirectional , which means that a second cable is required for the opposite direction.
In the optical variant, optoelectronic converters are used, which essentially consist of a photodiode ( wavelength approx. 650 nm). Technically, up to 20 Mbit / s are possible. The data direction is also unidirectional here. Numerous devices support a sample rate of up to 192 kHz, both optically and electrically.
Logical interface
S / PDIF and AES-3 have the following essential parameters:
- As a line code one is biphase mark code (BMC) is used.
- One block consists of 192 frames.
- A frame is in turn divided into two 32-bit subframes, each representing a sample .
- Each sample begins with a four bit - Preamble (B: 1. Channel block start, M: 1. Channel follower frame, W: channel sequence, sequence-frame), followed by status and up to 24-bit audio sample -Data.
- The data rate on the cable corresponds to 64 times the sampling rate and is 2.0 Mbps at 32 kHz, 2.8 Mbps at 44.1 kHz, 3.1 Mbps at 48 kHz and 6.2 Mbps at 96 kHz.
Multi-channel sound
Originally only two channels with PCM signals (32, 44.1 or 48 kHz, up to 20 bit) were transmitted via digital end user interfaces. However, other data can also be transmitted. To prevent interference with PCM-based devices, the SMPTE 337M standard defines the format in which specially coded multi-channel audio data such as AC-3 or DTS are transmitted.
A corresponding Dolby Digital / DTS hardware decoder is required to enable playback of compressed signals correctly on all speakers (5.1 / 6.1) . S / PDIF passthrough is the term used to describe the forwarding of compressed digital audio to an external hardware decoder. Uncompressed Mehrkanaltonübertragung is analogous only by a plurality of RCA - or jack possible. The digital transmission takes place via HDMI .
future
Because the maximum S / PDIF data rate (20 Mbit / s) is too low, a real-time downmix to lower data rates is necessary for newer audio formats such as Dolby Digital Plus or DTS-HD . B. only the DTS core integrated in the DTS-HD is transmitted. With a correspondingly lower sound quality, these sound formats can also be used via S / PDIF.
The S / PDIF data rate that is too low also does not allow PCM audio to output a sampling rate higher than 48 kHz with a dynamic range of 24 bits or 192 kHz optically on more than two channels. Sound formats that require more and should be output unchanged therefore require the use of the HDMI interface.
The importance of the S / PDIF interface is diminishing due to its limitations mentioned above; HDMI is the established replacement in consumer electronics.
Web links
Individual evidence
- ↑ Michael Dickreiter, Volker Dittel, Wolfgang Hoeg, Martin Wöhr: Handbook of Tonstudiotechnik . 8th edition. de Gruyter , 2014, ISBN 978-3-11-028978-7 , p. 688 f . ( limited preview in Google Book search)
- ↑ AES3-2003 . AES Standard for digital audio - Digital input-output interfacing - Serial transmission format for two-channel linearly represented digital audio data. Revised version of the AES3-1992 standard. Audio Engineering Society Inc., New York 2003.
- ↑ rme-audio.de, PDF, p. 9
- ↑ SMPTE 337M . Format for Non-PCM Audio and Data in an AES3 Serial Digital Audio Interface. Audio Engineering Society Inc., New York 2000.