I²S

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I²S, or Inter-IC Sound, or Integrated Interchip Sound, is an electrical serial bus interface standard used for connecting digital audio devices together. It is most commonly used to carry PCM information between the CD transport and the DAC in a CD player. The I²S bus separates clock and data signals, resulting in a very low jitter connection. Jitter can cause distortion in a digital-to-analog converter. The bus consists of at least three lines:

Bit clock line
Word clock line (also called word select line)
And at least one multiplexed data line

You may also find the following lines:

Master clock (typical 256 x bitclk)
A multiplexed data line for upload

[edit] Normal I²S

I²S consists, as stated above, of a bit clock, a word select and the data line. The bit clock pulses every time new data is placed on the lines. The bit clock will operate at 64*samplerate. So, for example, CD Audio (at 44.1kHz) will have a bit clock of 2.8224MHz. The word select clock lets the device know whether channel 1 or channel 2 is currently being sent, since I²S allows two channels to be sent on the same data line. Transitions on the word select clock also serve as a start-of-word indicator. Each channel can transmit up to 32 bits, so it is easy to see that the word select clock will operate at a frequency equal to the sample rate.

I²S data is sent from MSB to LSB, starting at the left edge of the word select clock, with one bit clock delay. There are left justified I²S streams, where there is no bit clock delay and the data starts right on the edge of the word select clock, and there are also right justified I²S streams, where the data lines up with the right edge of the word select clock.

I²S signals can easily be transferred via Ethernet-spec connection hardware (8P8C plugs and jacks, and Cat-5e and above cabling).