Site Contents

• Introduction
• Audio Data Format
• Interface Applications
• Hardware Specifications
• Data Transmission
• Digital-Analog Converter
• Resetting & Auto-Switching
• History & Characteristics
• Data & Cabling Details
• Coding Format
• Conversion Circuits
• Internal Connection
• External Connection
• Optical Output Circuit
• Transmission Line

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SPDIF: Interface Applications

Purposes

The interface has two main purposes. One is to transfer as per the IEC 61937 standard the compressed digital audio carrying the signal from/to output of a PC or DVD player and a Dolby Digital designed home theatre system referred as DTS surround sound. The other extensive use of SPDIF interface is inter-connection of professional or commercial audio equipments. Most DVD/CD-ROM drives contain SPDIF interface. Now external SPDIF output can also be found in high-end sound cards.

Advantage

SPDIF digital transmission has eliminated noise found in the earlier analog transmission and that is the main advantage of this interface. CD-ROM drive with inferior quality digital-analog converter used to produce undesired hissing and static noises. In signal transfer through analog format between CD-ROM drive and sound card, the connection cable often works as an antenna catching stray unwanted noises generated due to electromagnetic interference by the computer hardware. However this problem is got rid of by using SPDIF input sound card and SPDIF output CD-ROM drive instead of an analog connection. This is because the audio-digital conversion in case of SPDIF interface takes place from within the sound card and not within the CD-ROM drive. For this, only SPDIF input/output data cable is required.

Input/Output Connection

Shielded co-axial type cable is widely used to transmit SPDIF data through RCA jacks and plugs as these eliminate almost all kinds of audio noise. However with optical fibre cable for SPDIF, audio quality has further improved. Another advantage is the cable length. A much lesser length of optical fibre can carry same amount of signal compared co-axial cable. Though yet to find wide mainstream use in the consumer market because of cost factor, mini CD-ROM decks are growingly using this optical SPDIF I/O connection. Optical SPDIF connection usually consists of one SPDIF co-axial input and output, one co-axial output, two SPDIF optical inputs and one SPDIF optical output.