LRCLK

LRCLK, short for Left-Right Clock, is a control signal used in certain serial digital audio interfaces to frame and label sample data. It is most commonly associated with the I2S (Inter-IC Sound) bus, but the term is also used for the left-right or word-select clock in related formats.

Function and role: The LRCLK indicates which channel’s data is currently on the data line. Typically, one state designates the left channel and the opposite state designates the right channel. The exact polarity can vary by device and format, but the essential behavior is a regular alternation between left and right channel data within a frame.

Timing and relationship to data: In I2S, a data frame consists of left-channel data followed by right-channel data. LRCLK toggles once per frame, so its frequency equals the per-channel sampling rate (Fs). A channel’s MSB is usually presented after a one-bit delay from the LRCLK edge, which distinguishes I2S from some other formats such as left-justified or right-justified schemes. The accompanying bit clock (SCK or BCLK) drives the serial data, and its frequency is typically Fs multiplied by the number of bits per channel and by the number of channels.

Usage and interoperability: LRCLK is generated by the audio interface and used by DACs, ADCs, and digital signal processors to synchronize and demultiplex interleaved channel data. While common in I2S, not all formats use LRCLK; some employ different framing conventions or omit a word-select signal altogether. Correct interpretation of LRCLK polarity and timing is essential for interoperability between devices.

Summary: LRCLK serves as the left-right frame clock in I2S and similar formats, signaling channel boundaries and ensuring proper alignment of stereo data at the per-channel sampling rate.