SPDIF is a standard that was jointly developed by Sony and Philips, two media device companies. The acronym stands for Sony Philips Digital Interface or Sony/Philips Interconnect Format. The exact definition of the standard is defined under the IEC 958 type II, and S/P-DIF.
SPDIF refers to both the physical layer needed to transfer digital data between a media player device and speakers, and the Data Link Layer protocol specifications. The physical layer refers to all the physical and electrical specifications for devices, as well as the relationship between a physical medium and a device. On the other hand, the data link layer presents the procedural and functional means to transfer data. It can also detect and correct errors that may occur in the physical layer.
The data format and the physical layer are used to transport digital audio signals from CD players, DVD players, PC audio cards, car audio systems and such to speakers that will interpret them as sound.
SPDIF Audio Data Format
The SPDIF Audio Data Format is a component of the IEC-60958 standards. It is derived from the AES/EBU standard, with the IEC-958 type II as its designation.
It is a derived version of the original AES/EBU consumer standard. It is similar to AES/EBU at the protocol level, but it can function with cheaper hardware. The only difference between the S/PDIF and AES/EBU protocol is the Channel Status Bit. The Channel Status Bit is the designated portion of the digital audio data transmitted over IEC958 between hardware devices.
Both S/PDIF and AES/EBU include two 192 data words from the left and right channel data. SPDIF is divided into 12 words of 16 bits each, while AES/EBU is divided into 8 words of 24 bits each.
SPDIF Audio Data Rate
There is no given rate or resolution in the SPDIF protocol. The actual equipment containing the SPDIF connectors will verify the data rate from the SPDIF signal received by both pieces of audio hardware.
The SPDIF protocol uses the Bi-phase mark code that contains either 1 or 2 transitions for each bit. It allows the primary word clock to be extracted directly from the base signal.
Usually, the SPDIF data rates are 48 kHz in a Digital Audio Tape and 44.1 kHz in a stereo CD audio.
The transmission rate is limited to only 16-bit audio because of audio CD restrictions. However, there are some SPDIF protocols that support audio with over 20 bits.