Understanding the Master and Slave Functional Applications of I2S in Bluetooth Audio Modules

Update: April 15, 2025

By Han

Table of Contents

In the wireless audio field, Bluetooth I2S (Inter-IC Sound) technology is gradually becoming the core solution for high-fidelity sound quality. Unlike traditional Bluetooth audio, which suffers from secondary codec losses, Bluetooth I2S achieves nearly lossless wireless audio transmission through the collaboration of the master (Master) and slave (Slave) roles. So, what are the specific functions of the Bluetooth I2S master and slave? Let's dive into the analysis with the RHA Technology Bluetooth audio module (RHA-BT301M)!

Table of Contents

Master-Slave Mode Definition

Master Device: Responsible for generating the BCLK (bit clock) and LRCLK (frame clock), and controlling the data transmission timing.
Slave Device: Synchronizes data based on the clock signals from the master device, such as ADCs, DACs, etc.

Signal Line Connections

The I2S standard includes the following signal lines (some devices may omit MCLK):

Signal Line	Full Name	Description
BCLK	Bit Clock	Bit clock, determines the transmission rate of each data bit.
LRCLK	Left/Right Clock	Frame clock (audio selection), usually related to the sampling rate.
SD	Serial Data	Audio data stream (single-channel or bidirectional communication).
MCLK	Master Clock	Master clock (optional), typically 256/512 times the sampling rate.

Wiring Rules

Master → Slave:
- Master device BCLK output → Slave device BCLK input
- Master device LRCLK output → Slave device LRCLK input

Data Direction:

Master device sends data: Master device SD output → Slave device SD input (e.g., master control → DAC)
Master device receives data: Slave device SD output → Master device SD input (e.g., ADC → master control)

MCLK (optional):

If the slave device requires MCLK, the master device must provide it and connect it to the MCLK pin of the slave device.

Bluetooth Audio Module (RHA-BT301M) Wiring Diagram as Master

Bluetooth Audio Module (RHA-BT301M) Wiring Diagram as Slave

Note: MCLK is optional; if the slave device needs it, it should be provided; if not needed, it can be ignored.

Choosing Bluetooth I2S: Starting the Wireless Hi-Fi Era

Whether you are an audio device manufacturer or a user pursuing ultimate sound quality, the master-slave collaborative solution of Bluetooth I2S can bring a revolutionary experience upgrade. Say goodbye to the compromises of traditional Bluetooth and welcome the future of lossless, low-latency wireless audio. If you'd like to learn more, feel free to contact our technical support.

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Article by

Han

Han is a Operations and Marketing Specialist at LOYALTY-SECU.
With extensive expertise in wireless printing technology, cloud solutions, innovative product development, and Bluetooth module integration, I am dedicated to sharing company insights and industry knowledge to deliver unmatched value to our audience.

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