A pretty older application note about the serial audio interface by Cirrus Logic. Link here (PDF)
It may come as a surprise to those trying to make their initial investigation into audio systems design that there is a de-facto standard for transferring audio data within a system. Despite the differing naming conventions used within the industry, these apparently different interfaces are essentially identical. For the sake of simplicity, we will use the term Serial Audio Interface (SAI) in this discussion. The Serial Audio Interface is by far the most common mechanism used to transfer two channels of audio data between devices within a system; for instance, from the analogto-digital converter to the Digital Signal Processor (DSP) and then the digital-to-analog converter.