S/PDIF

Sony / Philips Digital Interface (S / PDIF) [ dɪdʒɪtəl ɪntəfeɪs ] is an interface specification for electrical or optical transmission of digital stereo or multi- channel audio signals between various devices for use in consumer electronics area.

S / PDIF is used for example in CD players, DAT recorders, MiniDisc at, between the DVD player and home theater receiver and digital audio cards in PCs. Also for audio systems in vehicles, it is used, where a complete wire harness can be replaced by a single fiber optic cable is also more sensitive to interference. Next are redundant as a term: Sony / Philips Digiconnect format, S / PDIF and TOSLINK also.

Connectors

S / PDIF (IEC 958:1989 earlier) defined in IEC 60958. In Germany, this standard is published as DIN EN 60958 in three parts.

The standard distinguishes between a professional ( professional mode, type I ) and an end-user mode (consumer mode, type II ). In domestic hi-fi equipment the consumer type is used. As a connector RCA connector ( coax ), optical TOSLINK or rarely use a 3.5mm jack to be used.

For the conversion of electrical / optical adapter with its own power supply is necessary.

The S / PDIF interface is closely related to the AES standard AES - 3, which is primarily used in professional studio range and colloquially referred to as AES / EBU. The main differences are in a different physical interface and the so-called channel state ("C bit" ) of the AES -3, which is used in the S / PDIF to the transmission of data copy protection. The rest of the data fields, in particular the format of the audio data, the structure of frames and sub-frames is identical between the S / PDIF and AES-3.

Physical interface

The physical interface at the S / PDIF is defined as an asymmetric connection with a voltage of approximately ± 0.5 volts at an impedance of 75 ohms. In contrast, the AES-3 interface has a symmetrical coupling according to the EIA- 422 ( RS-422) of 110 ohms characteristic impedance, and a voltage of about ± 5 volts. Usually XLR connectors are used for AES / EBU. Increasingly also twisted- pair cable, usually the Cat5 and higher are used.

S / PDIF and AES-3 have the following main parameters:

  • As the executive code Biphase mark code (BMC ) is used.
  • A block consists of 192 frames.
  • A frame is in turn divided into two subframes of 32 bits, each representing a sample.
  • Each sample begins with a four-bit preamble ( B: 1 channel block start, M: 1 channel sequence frame, W: Follow - channel, result - frame), followed by Status and up to 24-bit audio sample data.
  • The data rate is 2.0 Mbps at 32 kHz sampling rate, 2.8 Mbps at 44.1 kHz sampling rate, or 3.1 Mbps at 48 kHz sampling rate.

Multi-channel sound

Originally only two channels of PCM signals (32, 44.1 or 48 kHz, up to 20 bits) were transmitted via digital end-user interfaces. But also other data to be transmitted. This does not give rise to interference with PCM - based devices, is set the format in the standard SMPTE 337m are in the specially encoded multichannel audio data, such as AC -3 or DTS transferred.

In order to enable playback of compressed signals correctly on all speakers (5.1 / 6.1), is a corresponding Dolby Digital / DTS hardware decoder is required. S / PDIF pass-through is the name for the forwarding of the compressed digital sound to an external hardware decoder. Uncompressed Mehrkanaltonübertragung is analog only means of several RCA jack or possible digital recently via HDMI.

Future

Due to low data rate for a new audio data compression formats such as Dolby Digital Plus and DTS -HD, in these formats, a real-time down-mix is provided to lower data rates, so that S / PDIF, a signal can be output, but with a correspondingly lower sound quality.

In contrast to the two proprietary standards Dolby Digital HD and DTS HD Plus/AC-3 allows S / PDIF out bandwidth reasons, with PCM audio sample rates higher than 48 kHz with a dynamic range of 24 bits or optically 192 kHz to more than two channels issue. These formats require therefore the use of an HDMI cable to data rates of more than about 1.5 Mb / s.

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