Bluetooth Audio Transmission format: SBC ACC APTX LDAC

To achieve CD quality (16bit/44.1khz stereo) need 1411.2 kbit/s bandwidth, obviously Bluetooth A2DP cannot allow (Bluetooth 2.0/2.1 + EDR The largest carrier rate is about 2.1mbit/s, minus the protocol header, interference, power dissipation factor influence , the actual maximum transfer rate is approximately 1000bit/s), so the audio data needs to be compressed. We know that the same bit rate, different encoding format compression rate is different, thus decoding the quality of the restoration is different. A2DP Requirements must support SBC (Sub-band Coding) encoding, MP3, AAC, ATRAC are optional encodings, and other proprietary encoding formats can be used.

SBC: (Sub-band coding, sub-coded)

SBC is an encoded format mandated by the A2DP (Advanced Audio distribution profile, Bluetooth Audio Transfer Protocol) protocol. All Bluetooth devices support this protocol.
SBC is a low-complexity coding format with moderate compression ratios and a slightly lower sound quality at the same bitrate. Due to the limited bandwidth of wireless transmission, SBC encodes each sub-band to achieve the purpose of data compression, that is, after the SBC codec, the PCM data is changed. Supports sampling rates of 16kHz, 32kHz, 44.1kHz and 48kHz. Mono channel (mono channel), dual channel (DUAL channel), Stereo (stereo), combined stereo (Joint stereo) are supported. Data transfer rate 328kbps.
The headset as a receiving device (Sink) must support 44.1KHZ and 48kHz sample rates and need to support all channel modes.

Aac:

AAC, an acronym for Advanced Audio Coding, appeared in 1997 and was originally based on MPEG-2 's audio coding technology. Co-developed by Fraunhofer IIS, Dolby Laboratories, T, Sony and other companies to replace the MP3 format. In 2000, MPEG-4 standard was introduced, AAC re-integration of other technologies (PS,SBR), for the difference from the traditional MPEG-2 aac, so contains SBR or PS features AAC is also known as MPEG-4 AAC.
AAC is a new generation of audio lossy compression technology, in different fields, divided into nine kinds of specifications:
MPEG-2 AAC Main
MPEG-2 AAC LC (Low complexity)
MPEG-2 AAC SSR (Scalable sampling rate)
MPEG-4 AAC Main
MPEG-4 AAC LC (Low complexity)
MPEG-4 AAC SSR (Scalable Sample rate)
MPEG-4 AAC LTP (Long term prediction)
MPEG-4 AAC LD (Low Delay)
MPEG-4 AAC HE (High Efficiency) aacplusv1/v2 (3GPP)

AAC LC and AAC HE is now the most commonly used

The MPEG-4 AAC LC (Low complexity) is the most commonly used specification, we call it "lower complexity specification", we are referred to as "LC-AAC", which can find a balance point in the coding efficiency and sound quality of the medium bitrate. The so-called medium rate, refers to: 96kbps-192kbps between the code rate. Therefore, if you want to use the LC-AAC specification, please control the bitrate as much as possible in the previously said range. Within this interval, the LC-AAC can completely defeat the MP3 of the same bitrate with the lame highest quality slow coding mode. I think, whether it is Walkman, or Internet music transmission, it is recommended to use 128kbps-192kbps specifications of the LC-AAC encoding specifications.

MPEG-4 AAC HE (High Efficiency) aacplusv1/v2 (3GPP), we call "efficiency specifications", we are referred to as "HE-AAC" or "aacplus", this specification is suitable for low bit rate encoding, Because this kind of specification also integrates the kind of SBR technology in mp3PRO. When you need to encode an audio file between 32kbps-96kbps, it is recommended that you prefer the "HE-AAC" encoding specification. Using this specification, at the same rate, within this range, you can easily WMA9 and WMAPro, such as Microsoft's format to kill. If you are an audio fiction enthusiast, or a radio drama enthusiast, consider the HE-AAC specifications, even with a low bitrate, to provide a very clear voice dialogue effect.

APTX:

Official website: http://www.aptx.com/
APTX is a patent coding algorithm for CSR, and after being acquired by Qualcomm, APTX has a great deal of promotion in Android phones.
AptX is an efficient solution for wireless audio transmission via Bluetooth technology, and the AptX ensures consistent, high-quality audio through Bluetooth through high-performance, lossless compression algorithms. Aptx Technology was first born in the late 1980s and has been widely used by the music industry, major public broadcaster and film studios for many years.
Currently, AptX contains three technologies, including Aptx,aptx HD, AptX low Latency, which, according to the name, are traditional AptX, high-quality aptX, and lower-latency aptX, respectively.

• The APTX:APTX uses a high-performance, lossless compression algorithm that supports 48KHZ/16-bit LPCM audio data to deliver high-quality CD-level sound. Data transfer Rate 352kbps
• AptX hd:aptx HD uses Bluetooth to achieve high-bit HD (HD) sound. AptX HD supports 48khz/24 bit LPCM audio data, improved resolution also brings a lower signal-to-noise ratio, and significantly reduces distortion. AptX HD technology allows you to listen to the smallest detail in your music, providing lifelike sound that is indistinguishable from the actual sound of live performance. Data transfer rate 576kbps.
• Another disruptive technology in the AptX low Latency:aptx series is AptX, which provides high quality sound and low latency via Bluetooth. Low-latency, synchronized audio is critical to the experience of movies and games.

Support APTX mobile phone has a plus, Sony, Samsung, Huawei, Xiaomi, HTC, LG and other brands of mobile phones in some models, detailed product list please crossing network

Support Aptx headphones have OnePlus Bullets Wireless, Meizu Halo G20, sony some products, etc., detailed product list please crossing network

LDAC:

LDAC is a wireless audio coding technology developed by Sony, which was first unveiled at the CES Consumer Electronics exhibition in 2015. At the time, Sony said LDAC technology was three times times more efficient than standard Bluetooth encoding and compression systems. As a result, those high-resolution audio files will not be overly compressed when transmitting wirelessly, which can result in a great loss of sound quality.

When transmitting LPCM high-resolution audio, the LDAC technology maintains its maximum bit depth and frequency response range, delivering high-quality transmission even when the 96khz/24bit audio is reached. Compared with the traditional Bluetooth audio transmission technology, before transmitting LPCM audio, the first thing to do is to "degrade" the high-resolution video to 44.1KHZ/16 bit CD quality, and then after 328kbps transmission, equivalent to two times a large amount of information loss, The final quality is a far cry from CD quality.

The LDAC provides three modes of transmission, first of all the quality is the highest priority 990kbps mode, followed by the default 660 kbps normal mode, and finally the normal Bluetooth standard similar to the 330kbps mode, mainly to ensure the quality of the connection. In the Android O Developer Preview, we can see that LDAC also provides these three modes of transmission in this system.
Sony also licensed LDAC audio encoding technology to Google and natively supported on Android O, as long as the Android O-installed phone should be able to support LDAC. But it is not open to authorization, only the Sony home headphones are supported.

LDAC high code rate, poor anti-jamming ability, in the case of more interference need to reduce the code rate to maintain a stable connection

Summarize:

The Bluetooth audio transmission format is mainly for SBC and Aac,aptx and LDAC currently supports fewer devices and headphones. In the Bluetooth A2DP protocol, SBC is a must, and the other is optional. The iphone defaults to using AAC. Android uses SBC by default and some Android phones support aptx. Sony provides LDAC technology for Google Android O, which theoretically can use LDAC on Android 8.0 or more phones.

Reference:

Discussion on Bluetooth audio quality
Bluetooth Audio Transmission format: Acc,sbc,aptx and LDAC
Simple application of SBC Audio codec algorithm in wireless audio transmission
Basic knowledge of Bluetooth/classification, and audio ldac/aptx? hd
Something about Bluetooth headsets and Bluetooth audio
SBC coding in the Bluetooth protocol
A2DP Protocol Notes
AAC encoding
Introduction to AAC frame format and encoding
AAC Specifications (LC,HE,HEV2) and performance comparison
LDAC
a2dp-advanced Audio Distribution Profile-bluetooth
Bluetooth Core v5.0

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Bluetooth Audio Transmission format: SBC ACC APTX LDAC