Bluetooth aac means advanced audio coding; aac is the abbreviation of "Advanced Audio Coding", which is based on "MPEG-2" technology and has a sampling rate selection of "8 KHz" to "96 KHz", any With a bit rate and variable frame length, AAC is a high compression ratio audio coding that mainly adopts two strategies: discarding signal components that are irrelevant to the perception and removing redundant parts of the encoded signal.
The operating environment of this tutorial: Windows 10 system, DELL G3 computer.
AAC's full name is Advanced Audio Coding, advanced audio coding, born in 1997, based on MPEG-2 technology. Updated on the basis of MPEG-4 in 2000.
As the successor of mp3, the improvements of AAC compared to MP3 include: more sampling rate choices (8 KHz to 96 KHz, MP3 is 16 KHz to 48 KHz ); higher upper limit on the number of channels (48, MP3 is up to two channels in MPEG-1 mode, 5.1 channels in MPEG-2 mode); arbitrary bit rate and variable frame length.
AAC is a high compression ratio audio coding that mainly adopts two strategies: discarding signal components that are irrelevant to perception and removing redundant parts of the encoded signal. In fact, AAC encoding has the best effect below a bit rate of 128Kbps. Dolby Laboratories believes that the performance of the AAC format at a bit rate of 96Kbps exceeds that of the MP3 format of 128Kbps; at the same 128Kbps, the sound quality of the AAC format is significantly better. in MP3.
The commonly used bit rate for AAC in Bluetooth is 256Kbps. But there is one thing. Even if the AAC audio source is used, Bluetooth cannot directly transmit its original data stream. Instead, it first decodes AAC into PCM, and then encodes it into the AAC encoding supported by Bluetooth before transmitting. In terms of applications, the biggest supporter of AAC encoding is Apple. Devices such as iPhone, iPad, and AirPods all support AAC. Many music in iTunes software is also stored in AAC encoding format.
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Bluetooth (English: Bluetooth) is an open communication technology standard for wireless data and voice communication. It is a special short-range wireless technology connection based on low-cost short-range wireless connections to establish a communication environment for fixed and mobile devices. It is widely used in fields such as telecommunications, computers, networks, and consumer electronics. Bluetooth enables some of today's portable mobile and computer devices to connect to the Internet without the need for cables and to provide wireless access to the Internet.
Bluetooth is a protocol based on data packets and has a master-slave architecture. A master device can communicate with up to seven slave devices in the same piconet. All devices share the clock of the master device. Packet switching is based on a master-defined base clock that runs at intervals of 312.5 μs. Two clock cycles form a 625μs slot, and two time gaps form a 1250μs gap pair. In the simple case of single-slot packetization, the master sends information in even-numbered slots and receives information in odd-numbered slots. The opposite is true for slave devices. The packet size can be up to 1, 3, or 5 slots long, but in either case, the master will start transmitting from even-numbered slots and the slave will start transmitting from odd-numbered slots.
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