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: Audio Data Format
Data Transmission
Data in SPDIF is transmitted as 32-bit data word stream. For A and B channels, 192 data words each are transmitted. These 384 words make a data frame.
Specification & Standard
IEC standard 60958-3 defines SPDIF specification. This specification is recorded in German patent EP000000811295B1. The SPDIF audio data format has now become a part of a large standard called IEC-60958. Designated as Type-II IEC-958, this audio data format is also called AES/EBU standard. In fact AES/EBU consumer use standard is the original that uses cheaper hardware and SPDIF audio data format has just been an adaptation of AES/EBU. At the protocol level, both are identical.
Cables
The physical connectors earlier used for SPDIF were the professional audio equipment XLR. Now electrical co-axial cable RCA or optical fibre TOSLINK connectors are used. Signals transmitted over co-axial or optical SPDIF connectors are not different and carry the same information. Therefore choice of one over the other is made according to the convenience of the user. For consumer applications, these are more cost-effective and much simpler to use making them ideal for SPDIF cable. SPDIF cables have undergone change from 110 ohm balanced twisted pair to the more cost-effective and easily available 75 ohm co-axial cable. Use of more economical and more compatible RCA jacks and plugs instead of BNC connector (earlier used) and co-axial cables has tremendously improved the audio quality for consumers comparable with what was earlier found only in costly commercial equipment.
Channel Status Bit
Channel Status Bit defines the difference between AES/EBU and SPDIF protocols. Each sub-frame in AES/EBU has one channel status bit with each audio block having 192 bits or 24 bytes. In case of SPDIF, 16 bits each containing 12 words make a block of 192 bit. The first 6 bits in the first word is referred as Control Code. Different bits convey different meanings.