①, Bluetooth connection technology

Germany Bragi, which has been developing true wireless Bluetooth headsets since 2014, has been plagued by problems such as disconnection, binaural delay, and power consumption.  From 2017 to 2018, the Bluetooth technology transmission solution is still immature. Major manufacturers are focusing on solving Bluetooth technology transmission problems such as TWS headset Bluetooth disconnection and delay.  Apple AirPods uses exclusive Snoop (monitoring) patented technology to solve the problem of binaural connection delay asynchrony, even if it is expensive, it has been recognized by consumers, and sales have doubled year by year.

Apple AirPods' Snoop technology uses a monitoring mode, in which the secondary ear signal does not need to be forwarded by the primary ear, but monitors the signal sent by the mobile phone through certain rules, and finds the respective signals of the primary ear or secondary ear from the received signal  Therefore, problems such as interference caused by forwarding, system delay, and uneven power consumption of the primary and secondary ears are solved, and a good user experience is obtained.

The traditional Android system adopted the Relay mode in the early days. The binaural stereo was realized through the main ear forwarding. The audio was transmitted from the smartphone to the left earphone (master device), and then forwarded from the left earphone to the right earphone (slave device).  .  But it is facing the following problems: the Bluetooth signal forwarded by the main ear is easily interfered by other Bluetooth and WiFi signals; the forwarding itself will increase the system delay; and the forwarding signal passes through the human body.  In addition, due to forwarding, the power consumption of the primary ear is higher than that of the secondary ear. When the error code is required to retransmit the data packet, the power consumption of the primary ear will be overloaded.  The above reasons have caused many problems with connection stability, signal synchronization of the main and auxiliary headphones, and the length of standby of TWS headphones other than Apple. This is the main reason why Android TWS headphones cannot be compared with AirPods in recent years.

However, with the successive release of Qualcomm TWS + and Luoda Technology MCSync, the Android camp TWS headset can achieve independent connection of left and right channels, and its Bluetooth connection performance is comparable to Apple AirPods.

TWS headset Bluetooth connection technology comparison

② Related technologies that affect sound quality

Although Bluetooth technology has advanced to 5.0 in the consumer market, Bluetooth headsets still use the A2DP 1.2 (Advanced Audio Distribution Profile) standard developed by Bluetooth 2.1 for audio transmission.  Therefore, there is no qualitative difference in sound quality between listening to music with Bluetooth 5.0 and listening with Bluetooth 2.1.  In addition to physical hardware factors such as the material of the speaker, the sound quality of the TWS headset is mainly related to Bluetooth codec technology, the performance of the main control chip and the audio signal transmission method.

Although Bluetooth 5.0 technology provides greater communication capacity for audio, the improvement in sound quality is still in audio encoding.  CD sound quality requires a bandwidth of 1.41Mbit / s, which is limited by the transmission capacity of A2DP. Audio data needs to be encoded and compressed before being transmitted through A2DP, so audio transmission through Bluetooth cannot be completely restored, but only  Advanced compression technology to improve sound quality.  The current high-definition audio codec technology is mainly represented by Sony LDAC, Qualcomm aptX HD, and Huawei's HWA.

Sony officially launched LDAC high-resolution audio technology during CES in 2015, and opened the technology to Android 8.0 in 2017. The audio processing quality of this technology is very high, and it has become the standard compression technology for Android 8.0.  However, the premise of the encoder to achieve high-definition audio transmission is the bidirectional support of the sending end and the receiving end, and Android 8.0 supporting LDAC only solves the problem of the transmitting end, and the popularity of LDAC in the receiving end equipment (headphones, speakers, etc.) takes some time.  .

Compared with Sony LDAC, Qualcomm introduced the aptX HD high-definition Bluetooth audio codec technology in 2016 (supporting 24-bit / 48 khz audio), because of the foreshadowing of aptX (currently supported by about 4 billion devices, Qualcomm acquired CSR and acquired aptX  Technology), as well as Qualcomm's own advantages in the fields of chips and communications, have wider application potential.

In 2018, Huawei combined with key component suppliers and equipment vendors on the audio link to develop an end-to-end Bluetooth high-definition audio solution HWA (Hi-Res Wireless Audio). Its specifications are similar to LDAC and are also lossless.  Bluetooth audio encoding.  At present, HWA high-definition audio wireless transmission standards and industry alliances have also been established. Members include Edifier, Chinese Academy of Sciences Acoustics Institute, AKM, Sennheiser, HiFiMAN, 1MORE Wanmo, Huiwei, etc.

In addition, the new generation of Bluetooth technology standards continue to improve in terms of audio. In terms of audio decoder LC3, LE Audio integrates a new high-quality, low-power audio decoder LC3, and supports audio sharing.  This can not only optimize the transmission efficiency of Bluetooth, but also to a certain extent can further reduce the size of the TWS headset, will provide developers with greater flexibility, so that they can better design the product in terms of sound quality and power consumption.  There is a trade-off between product attributes.