I2S

The I2S Audio Interface provides a synchronous serial interface to off-chip audio devices.

The I2S or Inter-IC Sound Standard was developed by Philips to allow audio
data exchange between converters, filters and digital input/output interfaces.
The serial interface is a three-wire bus that contains a line for two time multiplexed
data channels (Data), a word select line (L/R clock), and a clock
line (Bit Clock).

The standard also dictates that the actual audio data be delayed by one Bit Clock period from the L/R clock.

 

This is the protocol used inside CD players to connect the transport and the DAC.

The major difference with SPDIF is that both sender and receiver use the same clock.

This eliminates input jitter.

Connecting

I2S is designed as a protocol between chips on the same board.
Some manufacturers use it to connect  boxes.

As there is no standard for cabling, each does it in his own way.

Even if both boxes have the same connector, if they are from different brands, the pin layout will be different too.

 

Some of us use I2S externally too, with good results. Like S/PDIF though, the devil is in the detials. The Transmission-lines must be terminated and the edge-rates must be fast in order to avoid adding significant jitter. Really low-loss high-bandwidth cables are required.

Audio Asylum

References

  1. I2S bus specification - Philips Semiconductors
  2. Inter-IC Sound Bus - Interfacebus.com
  3. DIGITabilis: crash course on digital audio interfaces - TNT-Audio
  4. I²S - Wikipedia