How do Bluetooth Speaker Work

What’s speaker workflow?

In Bluetooth speaker solution, the audio source will to DSP via analog, I²S and SPDIF interface. The Bluetooth speaker MCU will control the DSP via I²C, when the analog audio to amplifier, and speaker, we could listen the sound. 

What are the types of audio source input?

The audio source input includes Bluetooth, SPDIF, Line, FM, MIC+ Hybrid Audio

Speaker Block Diagram

What’s Bluetooth Transmission Protocol?

HFP/HSP: HSP is a call protocol, HFP is a call protocol with a hands-free function, two-way transmission, generally 8K sampling rate or 16K sampling rate two formats, the sound quality is poor, usually it’s used for making calls, not suitable for playing music

A2DP: Bluetooth audio transmission protocol, one-way transmission, generally 44.1K or 48K sampling, excellent sound quality

AVRCP: Control command, which is used to control the mobile phone, such as previous and next songs, pause playback, etc., and this is also the lyrics transmission protocol

PBAB: Phone Book Protocol, used to transmit the phone book address book

What’s Bluetooth audio coding format?

SBC: The earliest coding format, the sound quality is the lowest among all protocols, and the delay is the longest, about 200ms delay

AAC: The new generation of coding format, the sound quality is much better than SBC, the format supported by basic Bluetooth chips now has a relatively short delay, about 180ms

APTX: Qualcomm dedicated high-fidelity low-latency coding format, mainly APTX-LL (low delay, about 40ms), APTX-HD (high-fidelity, delay about 120ms) these two decoding formats

LDAC: Sony's proprietary format, one level higher than APTX, supports 96K sampling rate

What’s spdif?

Spdif is a technology of wired transmission. The sound quality is the highest protocol at present, and the delay and loss are very low. It is also called copper shaft.

What are digital and analog signals?

Digital signal: The signal that audio is stored, compressed, and transmitted through digital technology is a digital signal

a.       The digital signal has strong anti-interference ability and high fidelity, and is often used in scenes with high quality requirements

b.       The manufacturing cost of digital signals is high, and eventually it needs to be restored to analog signals

Analog signal: The sound signal sampled directly by the ADC is an analog signal

a.       The analog signal is easier to be interfered, and the transmission process is also easier to lose

b.       Analog signal processing is relatively simple, and even sound generators can be used directly, such as microphones

What is the difference between single ended and differential signaling?

A single-ended signal means that there is only one audio signal line, and the other one is directly replaced by a ground wire, which is called a single-ended signal. This method is based on the ground wire. If the ground wire is disturbed, it will directly lead to The audio source signal is interfered, and the ability to be interfered by this method is relatively poor

Differential signals are not referenced to the ground, but have only one signal line. Instead, the audio signal is output from two different lines through a certain function, which is less affected by the earth, the output is stable, and the anti-interference ability and sound quality effect will be greatly improved.

What are I²S and PCM?

1.Same as PCM, I²S is a format/interface for digital audio transmission. I²S is a bus standard developed by Philips for audio data transmission.

2.Normally I²S has 5 lines: SLCK, MLCK, SDIN, SDOUT, WS

SLCK: It’s the serial bit clock, also known as the I²S clock, is used to synchronize data transmission

MICK: It’s the main clock, generally 256 times or 386 times the sampling rate. This line can generally be omitted. Many defaults are 256 times, and the calculation can be done directly.

SDIN: Audio input interface

SDOUT: Audio output interface

WS: Left and right channel identification feet, high level is transmitting right channel sound, low level is transmitting left channel sound

3.Format of I²S: sampling rate + storage bits, such as 48K 16BIT

a. Master clock: During I²S audio transmission, a clock needs to be provided to synchronize the data on both sides. One end that provides this master clock is the master end, and the other end is the slave end.

b. Sampling rate: The number of times of sampling per unit time, which is also the number of times of sampling in 1 second. The higher the sampling rate, the better the audio quality and the less the loss.

c. Storage bit: The format of digital audio storage, generally composed of 16-bit, 24-bit, and 32-bit binary numbers

What’s DSP?

Storage bit: The format of digital audio storage, generally composed of 16-bit, 24-bit, and 32-bit binary numbers

What types of amplifiers?        

Amplifiers are generally divided into three types: analog output class AB power amplifiers, digital output class D power amplifiers, and mixed optional AB\D class power amplifiers. Among them, the sound quality of class AB is worse than that of class D, and D The class conversion rate will be relatively small, but the interference of class D to the peripheral circuit is relatively large. If there is an FM sound, the power amplifier of class D will lead to poor radio effect.

What’s speaker?

The speaker is the last component in the audio system to restore the sound. It mainly makes the sound louder and plays the sound. The power can be matched according to the needs of the power amplifier. Generally, a cavity made of wood or other materials will have a better effect, the speakers include high, medium and bass speakers, customers can select it.

Shenzhen Huayang Xinke Electronics Co., Ltd has a Bluetooth 5.1 audio module HY-BT301, this module support analog audio and I²S audio. For the high-quality Bluetooth Speaker, the module support AAC, LDAC, aptX, aptX HD, aptX LL, for more information, welcome contact us.