Four Bluetooth Audio Decoding Formats of QCC5125 Module

QCC5125 module HY-BT301C can support SBC, AAC, aptX, LDAC four kinds of Bluetooth audio decoding. What is the difference between these four audio decoding?

The SBC（Sub-band coding）

arliest format should be SBC, and SBC is the encoding format mandated by the A2DP (Advanced Audio DistribuTIon Profile) protocol. All Bluetooth will support this protocol, so all Bluetooth audio chips will also support this protocol. The specific parameters of the bit rate of SBC encoding during transmission have not been found. According to the information given by Sony's official website, it is: 328Kbps, 44.1KHZ.

This bit rate is actually similar to that of a high-quality MP3. However, because the Bluetooth transmission intermediate device needs to be transcoded, taking MP3 files as an example, the transcoding process is MP3-"PCM-"SBC-"PCM, each time transcoding will lose details, resulting in SBC's listening experience will be better than the original MP3 worse.

Advantages: It can take advantage of the different characteristics of the human ear (or human eye) to perceive signals of different frequencies, and use coarser quantization in parts where human hearing (or vision) is not sensitive, and use finer quantization in sensitive parts. Get better subjective auditory (visual) results. For example, the fundamental tones and formants of speech are mainly concentrated in the low frequency band, so more bits can be allocated to represent their samples; while the high frequency bands where fricatives and similar fricative noises occur can be allocated fewer bits, so that sufficient compression can be achieved. voice data.

The quantization noise of each sub-band is bound in this sub-band, so that the signal in the frequency band with less energy can be prevented from being masked by the quantization noise in other frequency bands.

The specific implementation of the filter cannot be an ideal bandpass, and its magnitude effect inevitably has a limited roll-off. Therefore, when dividing the sub-bands, only the sub-bands can be overlapped or there can be a certain gap between the sub-bands. The former will produce aliasing distortion if it is sampled at the Nyssler frequency, while the latter will cause the original part of the frequency band to be lost by filtering, and the reconstructed signal will be distorted. The solutions to this problem include orthogonal mirror filtering and time-domain aliasing elimination.

AAC (Advanced Audio Coding)

AAC appeared in 1997, based on MPEG-2 audio coding technology. Co-developed by Fraunhofer IIS, Dolby Laboratories, AT&T, Sony and other companies to replace the MP3 format. In 2000, after the emergence of the MPEG-4 standard, AAC re-integrated its characteristics and added SBR technology and PS technology. In order to distinguish it from the traditional MPEG-2 AAC, it is also called MPEG-4 AAC.

AAC, the full name of Advanced Audio Coding, is a file compression format specially designed for sound data. Unlike MP3, it uses a new algorithm for encoding, which is more efficient and has a higher "price ratio". Using the AAC format can make people feel that the sound quality is not significantly reduced, and it is more compact. Apple iPod, Nokia mobile phone support AAC format audio files.

Advantages: Compared with mp3, AAC format has better sound quality and smaller file size.

Disadvantages: AAC is a lossy compression format, and there is an "essential" gap in sound quality compared with the popular lossless formats such as APE and FLAC. In addition, USB3.0 with faster transmission speed and large-capacity MP3 above 16G are accelerating the popularization, which also makes the "small" halo on the AAC head no longer exists.

APTX

APTX is CSR's patented coding algorithm. After being acquired by Qualcomm, APTX has been widely promoted in Android phones.

aptX is divided into four types: aptX, aptX HD and aptX Low Latency, aptX Adaptive. Now QCC5125 Bluetooth module can support aptX, aptX HD and aptX Adaptive.

An audio coding algorithm developed by Queen's University in the 1980s that maintains high audio quality while maintaining high bit rate efficiency. As a professional wireless audio transmission solution, aptX is used in public broadcasting and movie audio, and now it is placed in consumer products. Thanks to efficient encoding, aptX makes the sound retain more details, and the actual listening experience is better than the previous two. The propaganda of aptX also claims that it can reach CD-level listening.

Apt-X is a digital audio compression algorithm based on sub-band ADPCM (SB-ADPCM) technology. The original algorithm was proposed by Dr. Stephen Smyth in the 1980s. Developed by Audio Processing Technology (now merged by CSR) company and named aptX.

The use of Apt-X is mainly concentrated in Bluetooth headsets and Bluetooth speakers, and both terminals and Bluetooth headsets and speakers must support Apt-X in order to play its functions. There is a certain delay in Bluetooth audio transmission. The biggest feeling is that the audio and video delay can be minimized.

LDAC 

LDAC improves the channel, and on devices that support LDAC, the communication bit rate of Bluetooth is close to 1M.

LDAC can transmit about 3 times the data of ordinary Bluetooth*1 (at the maximum transmission speed of 990kbps*2), so that when you enjoy Hi-Res Audio*3 music in wireless conditions, you can listen to music close to Hi-Res Audio sound quality.

At such a high transmission speed, it is possible to transmit lossless music. Of course, the transmission format of this near-proprietary protocol also results in only a small number of devices being compatible. But there is no doubt that LDAC has greatly improved the transmission rate, making the transmitted audio quality higher, and the sense of hearing is naturally the best.

LDAC is a wireless audio coding technology developed by Sony, which was first unveiled at the 2015 CES Consumer Electronics Show. At the time, Sony said LDAC technology was three times more efficient than standard Bluetooth encoding and compression systems. In this way, those high-resolution audio files will not be over-compressed during wireless transmission, so that the sound quality will be greatly lost.

The reason why Sony's decision is quite concerned is because LDAC technology was almost "Sony-only" in the past, only applied to its own mobile phones, players, headphones, and Bluetooth speakers. Because LDAC technology relies on the simultaneous support of the audio source and the speaker system, this technology is the exclusive highlight of Sony equipment. Now, as long as the mobile phone with Android O is installed, LDAC can be used to allow users to enjoy wireless high-definition music on the playback system that supports this technology.

Summarize

        SBC is the general audio format. When Bluetooth transmission does not support AAC and aptx, SBC is used for transmission. The sound quality is average. Now 80% of them are in this format;

        AAC, when Bluetooth supports files in AAC format and mobile phones also support AAC transmission, the sound quality is much better than SBC. Ordinary people can hear the difference.

        APTX is a lossless format for Bluetooth transmission. To support APTX, you must purchase this software fee, and aptx is not supported by all mobile phones. Generally, the supported mobile phones have the aptx logo on the back.

        For example, when your mobile phone is an iphone, your headphones or speakers also support AAC, and the playback format is naturally AAC; if your phone supports APTX, then your lazy bar and headphones also support APTX, and the playback format is natural. It's APTX, but at the same time, remember that your song itself is also lossless.

        These are not necessarily related, the big deal is that your Bluetooth supports APTX, AAC, SBC, but the format of your mobile phone is sbc, then the music played is naturally sbc. On the contrary, your mobile phone supports aac transmission, but your bluetooth only supports sbc, then the file played must be the sbc format file.

HYXKIOT Bluetooth 5.1 Audio Module HY-BT301C with QCC5125 chip, could support SBC, AAC, APTX, and LDAC audio decoding, could meet different wireless audio product audio decoding format requirement.