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Is the sound quality of the Bluetooth headphones not good? Part 2

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Is the sound quality of the Bluetooth headphones not good? Part 2

Bluetooth

Why is Bluetooth sound quality said to be poor?
Since Bluetooth headphones are connected wirelessly, the sound quality is said to be not as good as wired headphones.

bluetooth

The reasons for this are as follows.

There may be a delay in the voice
When transferring audio via Bluetooth, the sending device compresses the audio before making a call and the receiving data is decompressed again before playing the sound.

These occur instantly, but with a slight delay, this can manifest as a delay in the voice.

There are differences depending on the type of codec, headphone performance, distance and obstacles, but if there is a delay, the sound will not connect well and it will become unnatural, especially when watching a video, the image and the sound will match. how the disappearance occurs.

Insufficient codec capacity
The codec is an audio compression format, but compared to higher sound quality codecs like “LDAC”, “apt-X HD”, “apt-X” and “AAC”, it is connected with the standard codec ” SBC “. And the sound quality may be lower.

Note that it is pointless if one of the codecs is high performance and each device must support that codec.

If the headset or smartphone is a very old model, the sound quality may not be high due to insufficient codec capacity.

The latest Bluetooth headset situation.
It cannot be said that there are cases where there are problems with sound quality, but in recent years many high-quality and easy-to-use headphones have appeared, and headphones with specifications comparable to wired connections are attracting attention.

Let’s review the last situation.

Sound quality is improving
The Bluetooth version has also been updated, and the codec supports not only “SBC” but also “AAC” and “apt-X”, and the number of models that can enjoy music with high sound quality from Wireless way is increasing in recent times. years.

Make sure to choose headphones with multiple compression formats and high Bluetooth versions.

Easy to connect
It may seem that the connection (pairing) is more troublesome than wired headphones, but when pairing only for the first time, if the smartphone’s Bluetooth is ON the next time you use it, please turn on the headphones. Just connect it automatically.

You don’t have to plug and unplug the cable, and you don’t have to pull out your smartphone just to hear the sound.

Model with excellent resistance to water and impact.
The great advantage of Bluetooth headphones is that they do not get in the way during sports such as jogging because they have no cable and are difficult to break.

In such circumstances, I think the earbuds may have been spoiled by sweat or water droplets with conventional earbuds, but earphones with excellent water resistance that can be washed with water are also coming out.

You can confidently wear it for work and outdoor sports.

In this way, in recent years the latest models with improved quality and greater functions have appeared one after another in Bluetooth headphones.

When we think of sound quality as important, we think of wired headphones, but today, the number of Bluetooth headphones that are comparable to the wired types is increasing.

If you are thinking of changing models or replacing headphones, why not consider Bluetooth headphones?

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Is the sound quality of the Bluetooth headphones not good?

Is the sound quality of the Bluetooth headphones not good?

Bluetooth

Bluetooth headphones don’t need to be connected to wired smartphones, so there is less concern about cable disconnection, but many people wonder, “Isn’t the sound quality better than wired headphones?” .

Bluetooth

But what about reality?

Here, I would like to present the latest situation regarding Bluetooth headphones.

What is Bluetooth?
Bluetooth is one of the standards for short-range wireless communication and it communicates wirelessly like infrared and Wi-Fi communication.

Bluetooth devices are connected by a method called pairing and can communicate with each other.

Bluetooth has several factors that affect sound quality, such as radio wave strength, audio compression format, and transfer rate, and high sound quality can be maintained by keeping them at a high level.

Let’s explain each of the factors that affect sound quality.

Codec
A codec is an audio compression format for transferring sound over Bluetooth.

If you transfer the voice data to the headset as is, the amount of data will be too large and it will be difficult to communicate.

Therefore, a mechanism is adopted in which the sound is compressed on the sending side, the data is cleared and transmitted, and then the headphone side decompresses it to produce sound.

This audio compression format is called a codec and is divided into several methods.
The standard codec was called “SBC”, but high-quality codecs such as “AAC” and “apt-X” are now being adopted.

In addition, higher sound quality codecs such as “apt-X HD” and “LDAC” that can communicate at high resolution have also appeared in recent years.

However, the codec has the characteristic that it cannot be used unless the sender and receiver correspond to each other.

codec

Class
The class represents the strength of radio waves and is a measure of the communication range.

As of 2018, there are three kinds of Class 1.2.3, and general smartphones and Bluetooth headsets have adopted the standard called Class 2.

Class1 has a maximum communication distance of approximately 100m, Class2 has a maximum communication distance of approximately 10m, and Class3 has a maximum communication distance of approximately 1m. The greater the communication distance, the higher the power consumption.

If the devices are too far apart, communication errors are likely, which can lead to poor sound quality and skipping.

Bluetooth version
The Bluetooth version is fixed for each model and cannot be updated later.

The newer the version, the lower the power consumption, the greater the communication power and communication range, and the addition of extended functions.

As of 2018, the latest popular version is 5.0.

When buying Bluetooth headphones from now on, it is recommended to choose one with 4.2 or higher, which is widely used now.

Profile
A profile is a standard that defines what can be done with Bluetooth communication, and there are several types, such as those that can be operated simply by listening to the sound, those that can be operated as play and stop, and those that can be communicated. each other with a microphone. There is something.

There are four profiles used in Bluetooth headsets: “A2DP” which allows you to listen to music with stereo sound, “AVRCP” which allows you to control play and stop, and “HFP” and “HSP” which allow you to transfer and make and receive voice during a call.

Why is Bluetooth sound quality said to be poor?
Since Bluetooth headphones are connected wirelessly, the sound quality is said to be not as good as wired headphones.

Bluetooth sound bad?

Bluetooth sound bad?

Bluetooth

Today, everything is connected wirelessly and the wave is running in the world of audio.

Bluetooth

In particular, the technological progress of Bluetooth headphones and speakers is wonderful, and “wireless sound quality deteriorates” is said to be a thing of the past.

But is that true?

From a “convenience” standpoint, Bluetooth is very good. The nickname of smartphones is outstanding. However, when I consider it from the “sound quality” aspect, I am skeptical of its ability.

Therefore, this time, we will thoroughly investigate Bluetooth. How was Bluetooth born and what about the latest Bluetooth? We will introduce the good and bad sound quality.

Bluetooth overview
Bluetooth® is one of the short-range wireless communication standards for digital devices. It consists of Bluetooth Basic Rate / Enhanced Data Rate (BR / EDR) and Bluetooth Low Energy (LE).

The frequency channel used is the 2.4 GHz band. It is used in various products, mainly smartphones, PC-related devices, headphones, and speakers.

Especially in recent years, Bluetooth headphones have become very common in the city. The reason for its widespread use is that you can listen to the music played on your smartphone without a cable, and if you use Bluetooth, the headphones will not get tangled in the bag.

Bluetooth is also very popular when making calls while driving. If it is a hands-free call, you will not be charged with violating the use of mobile phones. Therefore, Bluetooth headset microphones that are very easy to use are very popular.

In addition, it is used for wireless communication of low-speed digital information, such as PC mouse and keyboard, such as notebook computers, text information, and voice information on mobile phones, PHS, smart phones, and tablets.

2. Derived from the name of Bluetooth
Bluetooth directly translates to “blue teeth”.
So why are the teeth blue? And what is the reason for that mark with the Bluetooth logo?

This chapter introduces the origin of the Bluetooth name and logo.

2-1. The godfather is Ericsson
The father of the name “Bluetooth” is an engineer from Ericsson (Telefonaktiebolaget LM Ericsson) in Sweden. A telecommunications equipment manufacturer based in Stockholm, Sweden, is a well-known manufacturer of fixed land equipment for mobile communications (mobile phones) in the world.

Approximately 20,000 engineers are engaged in research and development in 17 countries around the world, and the company is said to account for about 15% of annual R&D expenditures. Notably, GSM is used by more than 80%. of the world’s mobile phones and is practically the worldwide standard technology for wireless communication.

There is also a Japanese corporation called “Ericsson Japan Co., Ltd.” in Japan, which primarily provides ground binding equipment to SoftBank Mobile and EMOBILE. Due to such circumstances, Ericsson Japan Co., Ltd. has signed a helmet sponsorship contract with Fukuoka SoftBank Hawks since the 2012 season.

2-2. The motive is the king of Denmark “Harral Sprout Gormson”
Harald Blåt and Gormsen / Haraldr blátǫnn Gormsson is the first Danish king to negotiate a bloodless integration of Norway and Denmark to unite culture. The chronicle “Chronicon Roskildense” written in Latin around 1140 has the nickname of “Blue Tooth (in Danish: Blåtand, in English: Bluetooth)”, for which the King of the Blue Teeth There is a story that came to be called.

At the World Heritage site “Jelly Stones”, there is a runestone monument marking the achievement of the unification of Denmark by Haral. And, in relation to the achievements of Ericsson engineers, starting from the idea that “it will be a wireless communication standard that can be used in common in various fields regardless of the difference in industry and device”, Blåtand lo I called “Bluetooth” which is an English transliteration.

Bluetooth – the most convenient way to listen to music wirelessly. Part 2

Bluetooth – the most convenient way to listen to music wirelessly. Part 2

Bluetooth

Sound quality comparison of conventional Bluetooth coding

Bluetooth

⬤

SBC
Bluetooth “default” transmission code
SBC (Subband Codec) is an audio codec configured for the Advanced Audio Distribution Profile (A2DP) by the Bluetooth Special Interest Group (SIG), an organization that customizes various Bluetooth standards and specifications. Since it is part of the standard, almost all Bluetooth devices support it. SBC encoding. SBC supports mono and stereo transmission, with a sample rate of up to 48 kHz, while the highest bit rate for mono is 342 kbps and stereo is 345 kbps. The sound quality is approximately equal to that of medium quality MP3. SIG announced the SBC at CES in 2020. The following LC3 (Low Complexity Communication Codec) code, in theory, has better sound quality and less distortion than SBC.

⬤

AAC
The successor to MP3
Advanced Audio Coding (AAC) is a technology jointly developed by Dolby Lab, Sony, Nokia, and other major brands. It was designed as the successor to MP3. With the same bit rate, AAC is usually better than MP3. Sound quality. Spotify, Apple Music, and KKBOX use AAC encoding to stream music, and they are also widely used on different devices and platforms such as PS3, iPhone, and YouTube. Since iPhone, iPad, etc. will use AAC as Bluetooth music streaming, most headphones, speakers, etc. Bluetooth will support AAC, and the sound quality is roughly equal to medium to medium-high quality MP3.

⬤

aptX
The first “high sound quality” Bluetooth codec
aptX was also called “apt-X” before, but this encoding algorithm was invented as early as the 1980s and was eventually bought by the famous mobile phone processor manufacturer “Qualcomm”. aptX supports 16-bit, 44.1 / 48 kHz audio, bit rate up to 384 kbps, backward compatible with SBC. Since the bit rate is higher than that of SBC and AAC, it also has better sound quality.In the early years, it was the first Bluetooth music codec with slightly close to CD sound quality. However, due to the need to pay Qualcomm’s license fees, some devices, such as iPhones, are not equipped with aptX.

⬤

aptX-HD
Nearly “lossless” Bluetooth music streaming
aptX HD is an “evolutionary version” of aptX, which can provide a bit rate of up to 576 kbps and a bit depth of up to 24 bits and an audio stream with a sample rate of 48 kHz. Although the name has “HD”, it is still a lossy encoding method, but it can already provide almost lossless music quality, providing audio frequencies of up to 20 kHz and a dynamic range of at least 120 dB. And the encoding delay is quite small, which can be less than 5 milliseconds, which is especially beneficial for applications such as Bluetooth as hands-free communication. Of course, listening to music is helpful. In terms of high-quality Bluetooth transmission, the main opponent is LDAC developed by Sony.

Other readings:
▸ [SPILL Encyclopedia] aptX HD: The Evolution of High-Quality Bluetooth Music Listening
Bluetooth (Bluetooth) is believed to be the most familiar wireless way of streaming songs. Although the connection is quite convenient, the sound quality is slightly lower. However, with the upgrade of the Bluetooth version and technology, different codes have been introduced to make this connection method convenient and fast.

Bluetooth – the most convenient way to listen to music wirelessly.

Bluetooth – the most convenient way to listen to music wirelessly.

Bluetooth

Bluetooth (Bluetooth) is believed to be the most familiar wireless song transmission method.

Bluetooth

Although it is quite convenient to connect, it is a bit inferior in terms of sound quality compared to AirPlay, Chromecast, DLNA, Play-Fi, and other technologies that use network methods to stream music. However, with the version upgrade and Bluetooth technology, different codes have been introduced so that this convenient and fast connection method can also provide better and better sound quality.

Chi
Bluetooth (Bluetooth) is believed to be the most familiar wireless way of streaming songs. Although the connection is quite convenient, the sound quality is slightly lower. However, with the version upgrade and Bluetooth technology, different codes have been introduced so that this convenient and fast connection method can also provide better and better sound quality.
Version 1.0 to 5.2: Reduce Power Consumption, Increase Bandwidth, and Increase Features
This technology was developed by the telecommunications company Ericsson in the 1990s. After almost 30 years of development, Bluetooth has undergone many version changes. Bluetooth uses a radio frequency of 2.4GHz, from the initial Bluetooth 1.0 with a slow speed of 723.1kbps, to Bluetooth 3.0, it has increased considerably to 24Mbps, which is enough to transmit more data and higher quality music; the later Bluetooth 4.0, 4.1, 4.2 are It is a very popular version with much improved functions. Among them, version 4.0 adds Bluetooth low energy technology, version 4.1 adds smart connection and supports connection of multiple devices, version 4.2 can connect to the Internet, and even the current Bluetooth-enabled devices are quite similar and part of them they still use Bluetooth version 4.x.

Bluetooth (Bluetooth) is believed to be the most familiar wireless way of streaming songs. Although the connection is quite convenient, the sound quality is slightly lower. However, with the version upgrade and Bluetooth technology, different codes have been introduced so that this convenient and fast connection method can also provide better and better sound quality.
The AVR-X2600H amplifier released by Denon in 2019 still uses Bluetooth version 4.1, which is sufficient to support two-way Bluetooth and other functions.
Other readings:
▸ [Evaluation] Denon AVR-X2600H: Decentralization of real flagship machine technology!
Bluetooth 1.0
The original version of Bluetooth had quite a few compatibility issues, and was prone to crashing when connecting and leaking data. The speed of the later version 1.2 was increased to 723.1kbps, and the transmission distance was only 10 meters.

Bluetooth 2.0
With the incorporation of “skip-free narrow-band channel” (skip-free narrow-band channel) technology, there is no need to exchange feedback signals with each Bluetooth-connected device, so Bluetooth signals and data can be stream to multiple devices.

Bluetooth 3.0
The data transmission speed increases up to 24 Mbps, which is 8 times that of Bluetooth 2.0, which is enough to transmit high-quality music signals. The current conventional Bluetooth transmission speed is probably at this level. In addition, the power control has been improved to significantly reduce power consumption when idle.

Bluetooth 4.0
Although the speed remains the same as in 3.0, the transmission distance has been greatly increased to 50 meters, or even up to 100 meters, and three modes of “Bluetooth Low Energy”, “Traditional Bluetooth” and “Bluetooth” have been incorporated. Of high speed”. 4.2 is the most popular version of Bluetooth.

Bluetooth 5.0
It supports indoor positioning and navigation functions, combined with Wi-Fi to achieve indoor positioning with an accuracy of less than 1 meter. It is possible to receive unmatched data such as advertisements, location information, etc., the transmission speed increases to 48 Mbps, and many underlying optimizations have been made for the Internet of Things.

Bluetooth 5.0, released in 2016, doubles the bandwidth to 48 Mbps and supports features like indoor navigation and positioning. The recently announced Bluetooth 5.2 in 2020 adds LE Audio technology, running on Bluetooth Low Energy, which allows headphones to connect to multiple audios, or multiple sets of headphones to connect to one audio, using the LC3 (Audio Codec). low complexity communication

How Bluetooth Headphones Work Part 3

How Bluetooth Headphones Work Part 3

aptX BlueTooth

What is aptX, the savior of Bluetooth sound quality

Let’s take a look: if you compare a Bluetooth headset to a person, the Bluetooth chip is like your heart and aptX technology is like your eloquence. Whether the transmitted sound is smooth and clear, so that the listener can know what you mean is an important indicator.

With the chestnuts finished, let’s get back to the topic: What is aptX anyway? Now, let’s take a look at it from a technical point of view.

There is a word involved in Bluetooth transmission technology called “bit rate”, which is the number of bits transmitted per second, and the unit is bps (bits per second). In the case of transmitting the same audio file, the higher the bit rate, the faster the data transmission speed and the shorter the time required. There should be “chestnuts” here, like when Yao Ming was practicing, he had 100 basketballs at A, and he had to throw them into the basket at B. Under the premise of making all the shots, Yao Ming would take more basketballs each . (Bit rate) and the more basketballs (bit rate) you put in, the shorter the total time required.

But for Bluetooth technology, because it is limited by the maximum bandwidth available in transmission, it is not always suitable for transmitting high-quality audio.

For this reason, Bluetooth “guardian angel” -aptX technology was born. It recodes and decodes the audio to be transmitted, significantly reducing the bit rate, without affecting the sound quality and without the transmission delay, which makes the Bluetooth stereo listening experience a revolutionary leap. So with aptX, you can enjoy pure wireless audio with CD-level sound quality anytime, anywhere.

How Bluetooth Headphones Work Part 2

How Bluetooth Headphones Work Part 2

Bluetooth Aptx

Introduction to Common Abbreviations in English

aptX Bluetooth

NFC – Near field communication technology, Bluetooth headphones with this function can be quickly paired and connected by touching the playback device.

AAC: The technology provided by Dolby Laboratories is a high compression encoding algorithm. There is a lot of AAC audio in Apple Music and the sound quality is better than MP3 at the same bit rate. The iPhone will use AAC encoding for Bluetooth streaming. .

AptX – Qualcomm’s leading encoding technology, which is more efficient than traditional Bluetooth encoding and preserves more details in the sound. Most newer Android phones are equipped with AptX, but Bluetooth headsets must also be AptX-compatible to be effective.

LDAC – A Bluetooth transmission technology developed by Sony itself, which can transmit 3 times normal Bluetooth data and perform lossless music playback with Bluetooth, but only Sony devices support this technology.

Simply put, in terms of bit rate, AAC “AptX” LDAC. From the point of view of the audio source, if the player plays lossless music, the actual listening experience is AAC “AptX” LDAC, but since most users use network players such as NetEase Cloud or QQ Music, the source audio is mainly 128K. or 320K MP3, so there is no obvious difference in hearing between these encoding modes.

How to check if the phone supports aptx

Better to check the supported devices on the aptx official website.

APTX is a compressed streaming format that, while also lossy, can stream audio files with higher bit rates.

From a mobile phone point of view, APTX support requires mobile CPU support, but because this technology is paid, not all mobile phones have it. For example, Qualcomm Snapdragon 820 and 835 support APTX, but use Snapdragon 820. Mi 5 is Not Supported. Under normal circumstances, you can check for the APTX logo on the phone’s packaging:

Otherwise, you can call the after-sales consultation.

Of course, the safest way is to log into the APTX official website for inquiries. If submitting a link is not convenient for you, please use the official Baidu website. Go to the upper right corner of the official website and select Chinese, click Product search filter, the first is the brand, the brands in this list are compatible with aptx products (the list is sorted by English AZ , arranged vertically from left to right), the second One is the type of product: computers, mobile phones, headphones, speakers, etc. There are many types of products, the third is the aptx type, there are three types that are used in different fields. Please find your own brand and model of mobile phone, if it is not shown, it is not supported.

How Bluetooth Headphones Work

How Bluetooth Headphones Work

Bluetooth Headphones

The decoder chip of the mobile phone decodes music files such as MP3, generates a digital signal and sends it to the Bluetooth headphones via Bluetooth;

Bluetooth Headphones

The Bluetooth headset receives the digital signal and converts it to an analog signal that the human ear can understand through the digital-to-analog conversion chip inside the Bluetooth headset;

To amplify the analog signal, you must use the signal amplifier chip inside the earphone;

The headphone unit receives the amplified signal and makes a sound, and at this time, the ear hears the sound of music.

Do Bluetooth headphones ring?

However, the sound quality of Bluetooth headphones has long been criticized. The saying “Bluetooth headphones hear a sound” often circulates in the enthusiast circle. There are two main reasons for this:

When Bluetooth transmits audio data, it performs lossy compression on the audio, which loses sound quality;

Digital-to-analog conversion and amplification is done inside the Bluetooth headset. It’s hard to do both at the same time in such a small size, so for the sake of portability and price, sound quality is sacrificed even more.

The second point is the main reason. After understanding the principle of Bluetooth headphones, we know that for Bluetooth headphones to work properly, it is necessary to install batteries, Bluetooth modules, digital to analog conversion circuits, amplifier circuits, headphones. units, etc. in the headphone shell Series components, testing the manufacturer’s product design capabilities and comprehensive technical robustness. However, accomplishing this step only satisfied the need to “express”. If you want good sound, you should also tune in. This link should check the specific sound performance of the headphones with different materials, different diaphragms and different cables. In short, it is a more complicated process and the main R&D cost of the manufacturer.

Simply put, Bluetooth headphones are the product of compromise thinking, in order to get rid of the headphone cable shackles and reduce some of the sound quality. However, from today’s point of view, the sound quality of Bluetooth headphones made by traditional headphone manufacturers is generally better (of course, the price is also more expensive), which can meet the needs of most of users in terms of the appreciation of music, and the low-priced Bluetooth headphones produced by small manufacturers are in fact can only “hear” it.

Bluetooth codecs

Bluetooth codecs

Today, music playback over the Bluetooth protocol is gaining immense popularity.

This function is not only integrated into all modern audio systems. This algorithm is based on the operation of portable speakers and most models of wireless headphones. At the same time, the sound quality in practice can vary greatly, and here is why. The secret lies in the use of one or the other codec (not to be confused with profiles) when transmitting the source sound to the playback device. What codecs are there and what properties are they endowed with, let’s find out.

BLUETOOTH CODES

SBC (SubBand Codec) is a codec that is present in all devices without exception and provides basic sound quality, at the level of compressed files of an average bit rate.
AAC (Advanced Audio Codec) is an encoding algorithm based on a complex mathematical model. In terms of sound quality, it beats the SBC, but falls short of the next. It is used massively in Apple technology, which is why today it is the most preferred option for transmitting audio over Bluetooth.
AptX is an algorithm developed by Qualcomm with a sound quality similar to that of a CD. The source signal is compressed in a 4: 1 ratio with a 352 kbps bit rate and a 16 bit / 44.1 kHz bit rate. The AptX LL (low latency) variant with reduced playback delays stands out.
AptX HD is a further development of the AptX algorithm with the ability to transmit a signal with 24-bit / 48 kHz parameters. At the same time, the bit rate increases to 576 kbps. By ear, the differences to plain AptX are palpable, and the higher the class of technique, the more obvious the advantage of AptX HD.
AptX Adaptive is a new version (introduced in 2018) of the AptX codec, the key feature of which is the ability to compress audio with variable bit rate (dynamic quality setting). This is necessary in an environment where there are many “competing” wireless signals. In this case, it is possible to increase the compression of the original data to preserve the stability of the connection and, in the presence of “free air”, the sound quality will be maximum.
LDAC is a Sony creation and one of the highest quality codecs. The bit rate reaches 990 kbps at 24 bit / 96 kHz. By ear, this results in clear and dynamic music reproduction, free of digital artifacts. With the release of Android 8.0 Oreo, the LDAC codec has become part of this operating system as Open Source, but its presence on a particular device depends on the manufacturer of the gadget.
HWA (Hi-Res Wireless Audio) is a competitor of LDAC proposed by Huawei. The technology is based on the LHDC codec, developed by the Chinese Savitech, with a bit rate of up to 900 kbps and a maximum stream parameter of 24 bit / 96 kHz. In terms of sound quality, HWA is similar to LDAC, but so far the latter has a larger number of supported devices.
UAT (Ultra Audio Transmission) is the latest development from Hiby with a maximum bit rate of 1.2 Mbps and transmission parameters of up to 24-bit / 192 kHz. Due to the increase in the volume of data transmitted, UAT requires Bluetooth version 4.2 or higher. In order for the technology to work, any compatible Android smartphone with the Hiby Music app installed and a suitable receiver can be used, for example a compact Hiby W5 Bluetooth receiver.
BT-UHD (Bluetooth Ultra High-Definition Audio) is the next-generation protocol designed for maximum fidelity in high-resolution audio recordings. The maximum bit rate is 2.3 Mbit / s. Implemented for the first time on the Huawei Kirin A1 microprocessor using Bluetooth 5.1.
LC3 is the latest audio codec in the Bluetooth LE Audio specification, theoretically capable of delivering better sound quality than standard SBC at half the bit rate. As stated by the developers of the Bluetooth SIG (Special Interest Group) consortium, devices with LC3 will receive increased operating time (by reducing power consumption) and the ability to transmit the signal to multiple receiving devices at the same time (Broadcast Audio). Support for enhanced sync (multi-stream audio) is also noted. According to experts, the LC3 codec will be more relevant in wireless headphones, where one of the most important indicators is the battery life.

Modification of the Bluetooth stack to improve the sound in headphones without AAC, aptX and LDAC codecs

Modification of the Bluetooth stack to improve the sound in headphones without AAC, aptX and LDAC codecs

Some wireless headphone users notice poor sound quality and a lack of high frequencies when using the Bluetooth SBC standard codec, which is supported by all audio devices. A common recommendation for improving sound is to buy devices and headphones that support aptX and LDAC codecs. These codecs require license fees, so the devices that support them are more expensive.

It turns out that the poor quality of the SBC is due to artificial limitations of the Bluetooth stacks and the headphone configuration, and this limitation can be avoided on any existing device by software changes on the smartphone or computer.

SBC codec
The SBC codec has many different parameters that are negotiated during the connection establishment phase. Among them:

Number and type of channels: Joint Stereo, Stereo, Dual Channel, Mono;
Number of frequency bands: 4 or 8;
Number of blocks in a pack: 4, 8, 12, 16;
Quantization Bit Allocation Algorithm: Loudness, SNR;
The maximum and minimum value of the group of bits used for quantization (group of bits): usually 2 to 53.

The decoder MUST support any combination of these parameters. The encoder may not do everything.
Existing Bluetooth stacks generally match the following profile: Stereo set, 8 bands, 16 blocks, Loudness, bitpool 2..53. This profile encodes 44.1 kHz audio at 328 kbps.
The bitpool parameter directly affects the bit rate within a profile: the higher it is, the higher the bit rate and therefore the quality.
However, the bitpool parameter is not tied to a specific profile; Other parameters also significantly affect the bit rate: the type of channels, the number of frequency bands, the number of blocks. You can increase the bitrate indirectly by agreeing on non-standard profiles without changing the bit group.

SBC bit rate calculation formula

For example, dual channel mode encodes channels separately using the full bit set for each channel. By forcing the device to use Dual Channel instead of Joint Stereo, we get almost double the bitrate with the same maximum bitpool value: 617 kbps.
In my opinion, the use of a non-profiled bitpool value in the negotiation stage is a flaw in the A2DP standard, which led to an artificial limitation of the SBC quality. It would be more prudent to agree on the bitrate rather than the bit group.

These fixed Bitpool and Bitrate values originate from the table of recommended values for high quality audio. But the recommendation is no reason to limit yourself to these values.

SBC Bluetooth Profile Table

The A2DP v1.2 specification, which was active from 2007 to 2015, requires all decoding devices to function properly with bit rates up to 512 kbps:

The SNK decoder shall support all possible values of the bit combination that do not exceed the maximum bit rate. This profile limits the maximum bit rate available to 320 kb / s for mono and 512 kb / s for two-channel modes.

In the new version of the specification, there is no bit rate limitation. Modern headphones released after 2015 that support EDR are supposed to be able to support bit rates up to ≈730 kbps.

For whatever reason, the Bluetooth stacks I have tested for Linux (PulseAudio), Android, Blackberry, and macOS have artificial limits on the maximum value of the bitpool parameter, which directly affects the maximum bitrate. But this is not the biggest problem, almost all headphones also limit the maximum bitpool value to 53.
As I’ve already seen, most devices work fine on a modified Bluetooth stack with a 551 kbps bit rate, without any dropouts or crackles. But that bitrate would never be constant under normal circumstances, in normal Bluetooth stacks.

Modify the Bluetooth stack
Any Bluetooth stack that is compatible with the A2DP standard supports dual channel mode, but it cannot be activated from the interface.

Let’s add a switch to the interface! I made patches for Android 8.1 and Android 9 that add full dual channel support to the stack, add mode to the mode switch menu in developer tools, and treat dual channel SBCs as if they were an additional codec like aptX, AAC or LDAC (Android calls it HD Audio) by adding a check mark to the Bluetooth device settings.