SP/DIF transmitter project
| Project: SP/DIF transmitter project | |
|---|---|
| Featured: | |
| State | Completed |
| Members | Danny Witberg |
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| Description | This project describes a lightweight SP/DIF transmitter in VHDL |
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Introduction
SP/DIF is a protocol for sending and receiving digital audio over an optical or electrical transmission line. It is capable of sending two channels of up to 24 bits audio at a sample rate of up to 384kHz. However, most of the times you will encounter this protocol as 16 bit 44.1kHz, being the quality of a CD. Optical connector standard for SP/DIF is a TOSlink connector, developed by Toshiba. Electrical interface uses a cinch type connector.
SP/DIF is very similar to a professional standard, AES-EBU. In fact, only the signaling bit and their meaning is diffrent from SP/DIF. An SP/DIF transmitter can be connected to an AES-EBU receiver. However, from AES-EBU to SP/DIF can give unpredictable results.
Both AES/EBU and SP/DIF originate from the AES3 standard, developed by the Audio Engineering Society. It is a biphase mark encoded bitstream to ensure that signal integrity is maintained across the whole of the transmission line. Databits are sended as 10 or 01 sequence for a '1' bit, and 00 or 11 for a '0' bit.
A frame consisting of two subframes are sent every sample. Every subframe contains, apart from the audio data from a channel, a preamble, validity, user, channel status and parity bit. The preamble breaks the rules of the biphase mark encoding for synchronisation purposes.
Biphase mark encoding through NRZI
