I2S

I2S, or Inter-IC Sound, is a serial bus interface standard used for connecting digital audio devices such as codecs, DACs, ADCs, and microcontroller audio subsystems. It provides a simple, low-pin-count method for transferring PCM audio data between integrated circuits.

The standard uses three wires: a serial data line (SD), a bit clock line (SCK, also called BCLK), and a word select line (WS, also known as LRCK). The WS line indicates which channel is being transmitted (left or right) and toggles once per audio frame. Data is transmitted MSB first, with the MSB of each sample appearing on the data line one bit clock after the WS edge, creating a one-bit delay between the word select and the first data bit. The bit clock drives the timing of the transfer, and many devices also require a master clock (MCLK) for internal timing purposes, though it is not strictly part of the three-wire I2S bus in all implementations.

I2S supports various sample sizes (commonly 16, 20, 24, or 32 bits) and stereo channels, with the frame rate determined by the audio sampling rate and the number of bits per sample. The bit clock rate is the product of the sample rate, bits per channel, and number of channels. I2S is distinct from other formats such as left-justified or DSP-style interfaces, which align data differently relative to the word select signal; many devices implement I2S but may also support these alternative formats.

Originating from Philips (now NXP) in the 1980s, I2S has become a widely adopted standard in consumer and professional audio hardware, favored for its simplicity and compatibility across many digital audio components.