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: Hardware Specifications

AES/EBU Standard

In the professional audio field, AES/EBU is the commonly used standard for interconnection of professional audio equipments. SPDIF was developed from this standard. While they are same at the protocol level, the difference lies in physical connectors.

The Change

XLR connectors in case of AES/EBU gave way to electrical co-axial cable with RAC jack and in some cases optical fibres (EIAJ Optical or TOSLINK) in SPDIF. These cables are cheaper and simpler to use. The BNC connector of commercial application was replaced by the RAC jacks in the 75 ohm co-axial cable. The co-axial cables are more compatible and less costly compared to the 110 ohm balanced twisted pair used in AES/EBU. For all practical purposes, SPDIF may be considered a consumer-friendly version of AES/EBU format.

Co-axial/Optic Comparison

Using co-axial cable is more advantageous than TOSLINK cable when tight bends or connections more than 6 metres long are required since high light signals get reduced in TOSLINK resulting in reduced range. However unlike co-axial cables, TOSLINK cables are not vulnerable to RF Interference and Ground Loops. While cost factor induces use of any standard 75 ohm A/V cable for co-axial connections, TOSLINK optic cable is also getting cheaper and coming within affordability of consumers.

AES/EBU/SPDIF: Main Differences

The differences lie in respect of cabling, connector, signal level, sub code information and Resolution. In SPDIF, cabling is 75 ohm co-axial or fibre against 110 ohm shielded TP for AES/EBU (75 ohm co-axial can also be used). SPDIF connectors are RCA, BNC or TOSLINK whereas for AES/EBU these are 3-pin XLR, BNC or 25-pin D-Subminiature. AES/EBU gives signal level of 3 to 10 volt against 0.5 to 1 volt for SPDIF. In AES/EBU, sub code information is ASCII ID Text which is SCMS Copy Protection Info for SPDIF. Maximum resolution for AES/EBU is 24 bits. For SPDIF it is normally 20 bits and only optionally 24 bits.