Bluetooth technology is named after Harald Bluetooth, an ancient Viking king. And for the sake of God, don't ask why. It’s better to figure out the really important things: how it works, what it’s capable of, why it’s interesting—and why it’s not—to a music lover. And most importantly, what happens to the audio stream when it leaves the smartphone or tablet to reach wireless headphones or speakers via Bluetooth.

Today, it is impossible to imagine a smartphone, a tablet, or any other self-respecting mobile device without Bluetooth support. However, the technology itself was born much earlier than smartphones and tablets - back in 1994, and its original purpose was to replace the wires in the filling of telecommunication stations.

Initially, the “blue tooth” had a lot of problems with the speed and reliability of communication, energy consumption and compatibility between various devices, but over time the technology has grown, with each new version becoming noticeably faster, more economical and more capable.

In the photo, Harald I Bluetooth is baptized. According to legend (unconfirmed), the king united the Danish settlements into a single country. This fact became the idea for Bluetooth - to connect all devices with one protocol

Some improvements - for example, simplification of the “pairing” procedure in version 2.1 and a serious reduction in the load on batteries in the current version 4.0 - have made the daily life of music lovers noticeably more comfortable. The advent of NFC technology has brought even more comfort - in conjunction with it, Bluetooth does not require any ceremony at all in mutual recognition of the receiver and transmitter; it is enough just to touch the gadgets to each other. But in general, progress has had little effect on the quality of sound transmission: in the latest edition of Bluetooth, this process is arranged in the same way as in its version before last ten years ago. But how exactly?

35 blue teeth

Like the vast majority of other wireless interfaces, Bluetooth is based on the use of radio waves. To transmit information, the “blue tooth” uses radio frequencies in the region of 2.4 GHz - Wi-Fi routers, wireless computer keyboards and mice, some DECT phones and a lot of other equipment “graze” here.

How is Bluetooth different from many other wireless technologies? On the one hand, it has a relatively low range: its range of action does not exceed ten meters, and thick walls can further reduce this figure.

Interestingly, the Bluetooth logo consists of two Scandinavian runes: “haglaz” and “berkana” (analogues of the Latin letters H and B)

On the other hand - multifunctionality. “Blue tooth” can be used for a wide variety of purposes: from transferring photos to a laptop to sending documents for printing, from controlling external devices to streaming audio. It's no wonder that Bluetooth has so many different so-called. “profiles”, each of which ensures the performance of a particular task, defining the technical parameters of the interaction between the Bluetooth transmitter and receiver. The total number of profiles is measured in dozens (according to an article on Wikipedia, there are a basic 35), only three are responsible for sound transmission. How are they different from each other?

Bluetooth profiles HSP, HFP and A2DP

The first of the Bluetooth audio profiles is called HSP - Headset Profile. As the name suggests, it is designed to work with mobile headsets and is tailored for basic voice transmission with all the ensuing consequences: audio is allowed only in mono format and with a bitrate no higher than 64 kB/s. Compared to this sound, even compressed MP3s seem like a divine delight to the ears.

The second - HFP, Handsfree Profile - is a slightly more advanced version of the same profile. Its target audience is the same monophonic headsets, so stereo is still not supported, but the sound quality is slightly higher. However, this profile is still not suitable for listening to music.

As soon as A2DP appeared, many hi-fi manufacturers took notice. But before everyone else, there were small companies that made adapters, like the GOgroove BlueGate shown in the photo - a small box with a DAC and a headphone amplifier inside.

For this purpose, a special A2DP profile is provided - Advanced Audio Distribution Profile. It is he who is responsible for connecting mobile devices with wireless speakers and headphones. The A2DP profile allows the sound source to find a common language with wireless acoustics, and most importantly, it controls audio compression for sending over the “bluetooth” channel. This procedure cannot be avoided due to the low bandwidth of Bluetooth, but the level of compression, algorithms used for compression and, ultimately, losses in sound quality can vary noticeably. This is where, as they say, nuances arise.

The SBC codec squeezes rougher than MP3

As you know, sound can be compressed in different ways. With or without loss in quality, with low or high bitrate, with different settings, using different codecs. Instead of one of the ubiquitous codecs for compressing the audio stream, the A2DP profile by default uses its own Subband Coding compression algorithm - or, simply, SBC.

A comparison made by Brent Butterwood (author of About.com) shows the difference in what noise is produced when a tone is applied at 5, 10, 12.5 and 20 kHz. Blue line - aptX, green - SBC()

Sound processing using SBC methods has a lot in common with the well-known MP3 compression, but the priorities are structured somewhat differently: the main task is not so much to minimize sound losses, but to simplify calculations. Everything should be fast, simple and easy to do even for the flimsiest mobile processor.

As a result, SBC deals with sound without unnecessary ceremony - for example, frequencies above 14 kHz are simply cut off during conversion, as a result of which the frequency range is noticeably narrowed. It is not surprising that even with the same bitrate as MP3 (and SBC allows bitrates up to 320 kB/s), SBC-encoded audio sounds noticeably worse.

This graph shows the spectra when transmitting a 1 kHz signal through aptX (blue) and SBC (green), as well as 4 kHz - aptX (magenta) and SBC (red) ()

As a result, when using the default encoder, transmission via Bluetooth degrades the sound of not only uncompressed audio, but also regular mp3 files - after all, during wireless transportation they are first decoded and then compressed again, this time much more roughly. Fortunately, SBC is the main, but not necessarily the only, audio stream compression tool that A2DP has in its arsenal. There are other, more interesting proposals.

Advanced Audio Coding: advanced, but not perfect

The basic SBC codec with its modest musical capabilities is not the best way to attract the attention of music lovers to Bluetooth technology. That is why the developers of many blue-toothed devices, especially in the top segment, complete the A2DP profile with optional, more advanced audio compression tools. The most popular of these tools is the AAC algorithm.

Unlike the SBC codec, which is familiar only to those who like to delve deeper into the technical specifications of Bluetooth, the AAC abbreviation is well known to the general public. Still would! After all, this is the format used, for example, in iTunes. The initial goal of the algorithm developers was to surpass MP3 in sound quality at the same bitrates - it is no coincidence that its name stands for Advanced Audio Coding, “advanced audio coding.”

Due to more complex algorithms, AAC actually stores more musical information than mp3, and even more so SBC. It is not surprising that its inclusion in the set of codecs supported by the A2DP profile significantly improves the sound of Bluetooth speakers and headphones.

The main thing is to make sure that the AAC codec is supported by both “blue-toothed” devices: both the one that serves as an audio signal transmitter and the one that works to receive it. If only one of a pair of such devices can understand AAC encoding, the A2DP profile automatically rolls back to the base codec. With quite obvious consequences for the sound.

AptX codec: the best option for music lovers

Even more advanced audio compression is provided by the aptX codec, which is actively promoted by CSR in the Bluetooth wireless audio market. The creators promote it as a means for wirelessly transmitting music “in CD quality.”

The aptX codec has its own logo because it was developed and patented by CSR

In fact, this is not entirely true, although the algorithms underlying aptX, in their principle of operation, do indeed resemble lossless encoders that compress the audio stream without losing audio information. Among the advantages of aptX is the ability to transmit Bluetooth MP3 and AAC without additional processing, and therefore without sound degradation.

A special version of aptX Low Latency, tailored to the needs of gamers and movie buffs, also ensures minimal delay in signal delivery - which means watching a movie without the lines lagging behind the characters’ facial expressions.

The aptX codec provides audio transmission with a bitrate of up to 352 kB/s, does not cut off the upper case and expands the frequency range to a quite respectable 10 Hz - 22 kHz, but the high complexity of the algorithms used requires mobile processors to triple the computing power compared to the basic SBC. That is why aptX support is quite rare among blue-toothed devices, most often in the premium segment of smartphones.

However, in order to become the owner of a smartphone with aptX, you don’t have to shell out that much cash: the catalogs of Samsung, Sony, HTS and Asus contain many models that support the advanced codec, including quite affordable ones.

As with AAC, when connecting your audio source wirelessly to speakers or headphones, you should make sure that the aptX codec is supported by both devices. Only in this case can you be sure that you are really squeezing out the maximum of its musical potential from the “blue tooth”.

How does the A2DP Bluetooth standard work with wireless headphones and a headset on a phone?

Modern smartphones have the A2DP Bluetooth wireless information transfer standard. It is designed to distribute audio over the air to peripheral devices. The transmitter is a mobile phone, and the receiver is wireless headphones or a portable speaker. A2DP Bluetooth technology eliminates the hassle of wires that clutter your portable audio devices.

The main feature of the A2DP Bluetooth profile is low bandwidth, so before transmitting audio, the smartphone is forced to process the track in a special way to reduce its size. Popular codecs are SPC, MP3, ACC and others. It is important that the codec is supported by the headphones, otherwise the music will not play.

How to enable and use A2DP Bluetooth?

A2DP Bluetooth (Advanced Audio Distribution Profile) technology allows you to use wireless headphones, speakers and other portable equipment. The user is also able to control the playback of tracks via keys located on the body of the peripheral devices.

1. To start using A2DP Bluetooth communication, you need to activate the corresponding option in the smartphone settings. On Android gadgets, it is recommended to open the notification shade and simply activate Bluetooth.
2. The next step is to turn on the headphones. They should be charged and appear in the list of devices available for connection. Here you just need to select the desired headset and wait for the smartphone to synchronize.
3. After the described steps, you can use all the capabilities of wireless headphones - listen to music, adjust the playback volume, switch tracks.

The range of A2DP Bluetooth is approximately 10 meters, so it is advisable for the user to keep the headphones close to the phone. If you move a certain distance, the sound will be interrupted or transmitted with interference.

A2DP Bluetooth audio technology is a popular communication standard among smartphone owners. It allows you to use wireless headphones or portable speakers. There are no special settings for the user; everything works out of the box via regular Bluetooth and a wireless headset.

Mobile devices today serve not only for their intended purpose - making calls, but also as multimedia entertainment centers. On smartphones and communicators you can watch movies, create photo albums, play games, surf the Internet, and listen to music. They listened to music and will always listen to it. But today we will find out what mobile devices need, or rather, what functions and accessories a phone should support for such musical pleasure.

The first accessory with which you can listen to music on your smartphone is headphones.

- (from English hands-free) a system that allows you to talk and control the phone without using your hands. Most often used in cars. Essentially, these are devices that provide the ability to carry on a conversation without holding a mobile phone or communicator in your hand. Consists of an earpiece and a microphone. There are wired and wireless Hands free.

Wired headsets are connected to a mobile device using a cord. They, in turn, are divided into mono and stereo headsets. There are also multimedia Handsfree, which allow you to control the player of your mobile device.

The wireless headset connects to the mobile device using . It is capable of picking up a mobile phone signal at a distance of up to 10 m.

Bluetooth wireless technology has for some time been indispensable for equipping mobile phones with various external devices such as handsfree, external memory or wireless modems. Recently, Bluetooth headsets and headphones () have become increasingly popular. Some of them have the ability to work not only with mobile phones and PDAs, but also with other devices that do not have the Stereo Bluetooth protocol through adapters.

The advent of phones that support the ability to use wireless Bluetooth stereo headphones to listen to music has allowed their owners to feel the real joy of the complete absence of wires. However, the cost of such phones and Bluetooth headphones themselves does not allow us to talk about the widespread nature of this phenomenon.

Stereo Bluetooth headphones cannot work with a mobile device if the latter does not support the profile.

One of the stable trends in the development of mobile devices is the improvement of wireless communications, which provide the ability to connect to the Internet, local network, as well as various peripheral equipment (headphones, headsets, speaker systems, printers, etc.) and other nearby gadgets. Wireless communication technologies, as well as other components of mobile devices, are constantly evolving. New versions of specifications appear, bandwidth increases, the set of functions expands, etc. Thanks to this, high-quality development is ensured, without which technical progress is unthinkable. However, progress also has a downside: every year it becomes more and more difficult for users to understand what is the difference between different models.

Usually, from a brief description of a mobile device, you can only glean the names of the wireless interfaces with which it is equipped. The detailed specification usually contains additional information, in particular the versions of wireless interfaces (for example, Wi-Fi 802.11b/g/n and Bluetooth 2.1). However, this is not always enough to fully appreciate the wireless communications capabilities of the device in question. For example, to understand whether a particular peripheral device connected via Bluetooth will work with the smartphone or tablet you have at your disposal.

In this article we will talk about various nuances that you need to pay attention to when assessing the capabilities of devices equipped with a Bluetooth interface.

Scope of application

A wireless interface with a short range, called Bluetooth, was developed in 1994 by engineers of the Swedish company Ericsson. Since 1998, the development and promotion of this technology has been carried out by the Bluetooth Special Interest Group (Bluetooth SIG), founded by Ericsson, IBM, Intel, Nokia and Toshiba. To date, the list of Bluetooth SIG members includes more than 13 thousand companies.

The introduction of Bluetooth into mass market consumer devices began in the first half of the last decade. Currently, many models of laptops and mobile devices are equipped with built-in Bluetooth adapters. In addition, a wide range of peripheral devices (wireless headsets, pointing devices, keyboards, speaker systems, etc.) equipped with this interface are on sale.

The main function of Bluetooth is the creation of so-called personal networks (Private Area Networks, PAN), which provide the ability to exchange data between nearby (within the same house, premises, vehicle, etc.) desktop and laptop PCs, peripheral and mobile devices and etc.

The main advantages of Bluetooth over competing solutions are low power consumption and low cost of transceivers, which allows it to be integrated even into small-sized devices with miniature batteries. In addition, equipment manufacturers are exempt from paying licensing fees for installing Bluetooth transceivers in their products.

Connecting devices

Using the Bluetooth interface, you can connect two or several devices at once. In the first case, the connection is carried out according to the “point-to-point” scheme, in the second - according to the “point-to-multipoint” scheme. Regardless of the connection scheme, one of the devices is the master, the rest are slaves. The master device sets the pattern that all slave devices will use and also synchronizes their operation. Devices connected in this way form a piconet. One master and up to seven slave devices can be combined within one piconet (Fig. 1 and 2). In addition, it is possible to have additional slave devices in the piconet (more than seven) that have a parked status: they do not participate in data exchange, but are in synchronization with the master device.

Rice. 1. Piconet diagram,
connecting two devices

Rice. 2. Piconet scheme,
combining several devices

Several piconets can be combined into a distributed network (scatternet). To do this, a device operating as a slave in one piconet must act as a master in another (Fig. 3). Piconets that are part of the same distributed network are not synchronized with each other and use different patterns.

Rice. 3. Diagram of a distributed network including three piconets

The maximum number of piconets in a distributed network cannot exceed ten. Thus, the distributed network allows you to connect a total of up to 71 devices.

Note that in practice the need to create a distributed network rarely arises. With the current degree of integration of hardware components, it is difficult to imagine a situation where the owner of a smartphone or tablet would need to connect more than two or three devices simultaneously via Bluetooth.

Radius of action

The Bluetooth specification provides three classes of transceivers (see table), differing in power, and therefore in effective range. The most common option, which is used in most currently produced mobile electronic devices and PCs, are Bluetooth Class 2 transceivers. Low-power Class 3 systems are equipped with medical equipment, and the main area of ​​application for the most “long-range” Class 1 modules are monitoring and control systems for industrial equipment.

Of course, you can count on a stable wireless connection between devices located at a maximum distance (for example, 10 m in the case of Class 2 transceivers) only if there are no large obstacles between them (walls, partitions, doors, etc.). The actual operating range may vary depending on the characteristics of the room, and on the presence of radio interference and sources of strong electromagnetic radiation on the air.

Bluetooth versions and their differences

The first version of the specification (Bluetooth 1.0) was approved in 1999. Shortly after the intermediate specification (Bluetooth 1.0B), Bluetooth 1.1 was approved - it corrected errors and eliminated many of the shortcomings of the first version.

In 2003, the Bluetooth 1.2 core specification was approved. One of its key innovations was the introduction of the Adaptive frequency-hopping spread spectrum (AFH) method, which made the wireless connection much more resistant to electromagnetic interference. In addition, it was possible to reduce the time spent performing device discovery and connection procedures.

Another important improvement in version 1.2 was the increase in data exchange speed to 433.9 Kbps in each direction when using asynchronous communication over a symmetric channel. In the case of an asymmetric channel, the throughput was 723.2 Kbit/s in one direction and 57.6 Kbit/s in the other.

An improved version of Extended Synchronous Connections (eSCO) technology has also been added, which improves the quality of streaming audio by using a mechanism to resend packets damaged during transmission.

At the end of 2004, the Bluetooth 2.0 + EDR basic specification was approved. The most important innovation of the second version was the Enhanced Data Rate (EDR) technology, thanks to the implementation of which it was possible to significantly (several times) increase the interface throughput. Theoretically, using EDR allows you to achieve a data transfer rate of 3 Mbit/s, but in practice this figure usually does not exceed 2 Mbit/s.

It should be noted that EDR is not a required feature for transceivers that comply with the Bluetooth 2.0 specification.

Devices equipped with Bluetooth 2.0 transceivers are backward compatible with previous versions (1.x). Naturally, the data transfer speed is limited by the capabilities of the slower device.

In 2007, the Bluetooth 2.1 + EDR basic specification was approved. One of the innovations implemented in it was the energy-saving technology Sniff Subrating, which made it possible to significantly (from three to ten times) increase the battery life of mobile devices. The procedure for establishing communication between two devices has also been significantly simplified.

In August 2008, basic additions (Core Specification Addendum, CSA) to the Bluetooth 2.0 + EDR and Bluetooth 2.1 + EDR specifications were approved. The changes made are aimed at reducing energy consumption, increasing the level of protection of transmitted data and optimizing procedures for identifying and connecting Bluetooth devices.

In April 2009, the Bluetooth 3.0+HS core specification was approved. The abbreviation HS in this case stands for High Speed. Its main innovation is the implementation of Generic Alternate MAC/PHY technology, which provides the ability to transfer data at speeds of up to 24 Mbit/s. In addition, it is planned to use two transceiver modules: low-speed (with low power consumption) and high-speed. Depending on the width of the transmitted data stream (or the size of the transmitted file), either a low-speed (up to 3 Mbit/s) or a high-speed transceiver is used. This allows you to reduce power consumption in situations where high data transfer rates are not required.

The Bluetooth 4.0 core specification was approved in June 2010. The key feature of this version is the use of low energy technology. Reduced power consumption is achieved both by limiting the data transfer rate (no more than 1 Mbit/s) and by the fact that the transceiver does not operate constantly, but is turned on only for the duration of data exchange. Contrary to popular belief, Bluetooth 4.0 does not provide higher data transfer speeds than Bluetooth 3.0+HS.

Bluetooth Profiles

The ability of devices to interact when connected via Bluetooth is largely determined by the set of profiles that each of them supports. A particular profile provides support for certain functions, such as transferring files or streaming media, providing a network connection, etc. See the sidebar for information about some Bluetooth profiles.

It is important to understand that you can use a Bluetooth connection to perform any task only if the appropriate profile is supported by both the master and slave devices. Thus, it is possible to transfer a “business card” or a contact from one mobile phone to another via a Bluetooth connection only if both devices support the OPP (Object Push Profile) profile. And, for example, to use a mobile phone as a wireless cellular modem, it is necessary that this device and the computer connected to it support the DUN profile (Dial-up Networking Profile).

Situations often arise when a Bluetooth connection is established between two devices, but some action (say, transferring a file) cannot be performed. One of the likely reasons for such problems may be the lack of support for the appropriate profile on one of the devices.

Thus, the set of supported profiles is an important factor that must be taken into account when assessing the capabilities of a particular device. Unfortunately, some mobile device models support a minimal set of profiles (for example, only A2DP and HSP), which significantly limits the ability to wirelessly connect to other equipment.

Note that the set of supported profiles is determined not only by the specifics and design features of the device, but also by the manufacturer’s policy. For example, some devices block the ability to transfer files of certain formats (images, videos, e-books, applications, etc.) under the pretext of fighting piracy. True, in reality, it is not lovers of counterfeit media content and software who suffer from such restrictions, but honest users who are forced to transfer even photos taken with their own built-in camera to a PC in a roundabout way (for example, by sending the necessary files to their own email address).

Bluetooth Profiles A2DP(Advanced Audio Distribution Profile) - provides transmission of a two-channel (stereo) audio stream from a signal source (PC, player, mobile phone) to a wireless stereo headset, speaker system or other playback device. To compress the transmitted stream, the standard SBC (Sub Band Codec) codec or another defined by the device manufacturer can be used. AVRCP(Audio/Video Remote Control Profile) - allows you to control standard functions of TVs, home theater systems, etc. A device that supports the AVRCP profile can act as a wireless remote control. Can be used in conjunction with A2DP or VDPT profiles. BIP(Basic Imaging Profile) - provides the ability to transmit, receive and view images. For example, it allows you to transfer digital photos from a digital camera to the memory of a mobile phone. It is possible to change the sizes and formats of transmitted images, taking into account the specifics of connected devices. BPP(Basic Printing Profile) - a basic printing profile that provides the transfer of various objects (text messages, business cards, images, etc.) for output on a printing device. For example, you can print a text message or a photo from your mobile phone to a printer. An important feature of the BPP profile is that on the device from which the object is sent for printing, it is not necessary to install a specific driver for the existing printer model. DUN(Dial-up Networking Profile) - provides a connection to a PC or other device to the Internet via a mobile phone, which in this case acts as an external modem. FAX(Fax Profile) - allows you to use an external device (mobile phone or MFP with a fax module) to receive and send fax messages from a PC. FTP(File Transfer Profile) - provides file transfer, as well as access to the file system of the connected device. A standard set of commands allows you to navigate the hierarchical structure of the logical drive of a connected device, as well as copy and delete files. GAVDP(General Audio/Video Distribution Profile) - provides transmission of audio and video streams from the signal source to the playback device. It is basic for A2DP and VDP profiles. HFP(Hands-Free Profile) - provides connection of hands-free car devices to a mobile phone for voice communication. HID(Human Interface Device Profile) - describes protocols and methods for connecting wireless input devices (mice, keyboards, joysticks, remote controls, etc.) to a PC. The HID profile is supported in a number of models of mobile phones and PDAs, which allows you to use them as wireless remote controls to control the graphical interface of the OS or individual applications on a PC. HSP(Headset Profile) - allows you to connect a wireless headset to a mobile phone or other device. In addition to transmitting the audio stream, functions such as dialing, answering an incoming call, ending a call and adjusting the volume are provided. OPP(Object Push Profile) - a basic profile for sending objects (images, business cards, etc.). For example, you can transfer a list of contacts from one mobile phone to another or a photo from a smartphone to a PC. Unlike FTP, the OPP profile does not provide access to the file system of the connected device. PAN(Personal Area Networking Profile) - allows you to combine two or more devices into a local network. In this way, you can connect several PCs to one with Internet access. In addition, this profile provides remote access to a PC that acts as a master device. SYNC(Synchronization Profile) - used in conjunction with the basic GOEP profile and synchronizes personal data (diary, contact list, etc.) between two devices (for example, on a desktop PC and a mobile phone).

Manufacturers constantly convince consumers that new solutions are certainly better than old ones. New processors have higher performance and lower power consumption compared to their predecessors; new displays have higher resolution and wider color gamut, etc. However, it is hardly advisable to use such an approach to evaluate the capabilities of the Bluetooth interface.

First, it is necessary to take into account the features of the existing fleet of Bluetooth devices. After all, as already mentioned, the maximum data transfer rate is determined by the device equipped with the oldest version of the interface. In addition, high data transfer rates are not required for all tasks. If this is a really important factor for copying media files (sound recordings, images) or broadcasting an audio stream with a low degree of compression, then for normal interaction of the phone with a wireless headset or for exchanging contacts with another device, Bluetooth 2.0 capabilities are quite sufficient.

Secondly, in many cases, a much more important factor than the maximum speed of the wireless connection is the set of supported Bluetooth profiles. After all, it is he who actually determines the range of equipment with which the existing device is capable of interacting. Unfortunately, this information is rarely provided even in the full specification of the device, and often you have to look for it in the text of the instruction manual or on user forums.

In the age of modern technology, you won’t surprise anyone with wireless devices: we actively use Wi-Fi on phones and laptops, connect wireless mice and keyboards to computers, and listen to music through Bluetooth headphones. And here comes the rub - how to choose the best headphones specifically for your devices, since there are quite a lot of audio transmission protocols over BT, and not all of them are supported by both the headphones and the device itself?

History and characteristics of the Bluetooth standard

But we will start, as usual, in the history of the creation of BT. And it began to be created, which is noteworthy, several years before USB - back in 1994, Ericsson, a fairly well-known manufacturer of telecommunications equipment at that time, began working on this standard. The standard itself was developed as a wireless alternative to a wired connection via RS-232 (better known as a serial port). The specifications themselves were ready by 1998 - at the same time the Bluetooth SIG group was created, which, together with Ericsson, included IBM, Intel, Nokia and Toshiba. In 2002, Bluetooth became part of the IEEE 802.15.1 standard (Wi-Fi, let me remind you, is part of the IEEE 802.11 standard). There are currently more than 18,000 companies in the Bluetooth SIG, making Bluetooth one of the few major standards for short-range data communications.

How does Bluetooth work? It, like Wi-Fi and many other systems, operates in the ISM range - from 2.4 to 2.4835 GHz. Of course, using one band leads to interference (overlap) of signals - and this, in turn, negatively affects the stability and speed of operation. Taking into account the fact that sound must always be transmitted in the same quality without delays, the developers of the standard used a trick. Perhaps the most important problem for BT is Wi-Fi - there are many such networks in the 2.4 GHz range in every home, and in total there can be 13 channels in this range with a width of 22 MHz:


Here the approach is simple: both the transmitter and the receiver always use one fairly wide channel. Yes, it may overlap with other channels, which will negatively affect speed, but not stability - and this suits everyone. Bluetooth uses a different approach: in the ISM range it has as many as 79 channels (in some countries 23 - but Russia is not one of them) with a width of only 1 MHz, and the receiver and transmitter change the channel at a frequency of 1600 times per second according to a given algorithm :


This is done specifically in order to greatly reduce the likelihood of signal interference in such a small frequency range. But this does not cancel interference - small BT channels may well fall into large Wi-Fi channels, and this will lead to a loss of speed, which is unacceptable for high-quality sound transmission. Therefore, BT uses AFH (Adaptive Frequency Hopping) technology. Its principle is that when changing Bluetooth channels, those channels that fall into a large Wi-Fi channel are ignored:


So if you use Bluetooth in one place, then in theory there are no problems with sound transmission - free channels will be selected from 79 channels, which will ensure sufficient speed. If you move around, then problems may arise - but, on the other hand, have you often seen Wi-Fi networks on the street? So the technology for transmitting audio over BT can be considered completely noise-resistant, and all that remains is to figure out the standards for transmitting audio over it.

Bluetooth profiles for audio transmission

The very first profile appeared along with the Bluetooth 1.2 standard more than 15 years ago - even then it occurred to the developers of the standard that wireless sound was great. Alas, the standard itself, called HSP - Headset Profile, was poorly suited for listening to music: sound transmission was in mono format with a bitrate of up to 64 kb/s. This was more than enough for headsets to work - for them, this profile, in general, was created - but music transmitted in this format sounded much worse than the crooked 128 kb/s mp3 played through the speaker of phones of that time.

The next profile was called HFP (Hands-Free Profile), and, as the name suggests, it was again intended for headsets - the same mono sound with low quality. Among the improvements is more advanced work: for example, when making a call, it was possible to transmit sound from the phone to the car speakers, and use the microphone in the car to answer. But we are interested in the transmission of music, and for obvious reasons this profile is categorically not suitable for it.

The first profile designed specifically for stereo sound transmission was A2DP - Advanced Audio Distribution Profile. It was in it that the function of polling headphones connected to the device appeared in order to find a common codec for them, and, most importantly, it was in this profile that it became possible to control audio compression: alas, compression cannot be avoided due to the low bandwidth of Bluetooth, but that’s it Compression varies greatly depending on the codecs used and the version of BT, so the resulting audio quality can vary greatly.

SBC codec - worse than MP3, but in stereo

If it is said that your wireless speakers or headphones support A2DP and not a word more, then most likely the SBC (Subband Coding) codec will be used for compression. The encoding principle itself is similar to MP3, but here the emphasis is not on minimizing sound losses, but on simplifying calculations, so that compression occurs very quickly even on weak mobile processors. Therefore, for example, frequencies above 14 kHz are completely cut off. Therefore, although SBC allows bitrates up to 345 kb/s, MP3 at 320 kb/s will sound significantly better - just look at the spectra:


As you can see, AptX delivers the best sound (more on it below), followed by MP3, and SBC in last place.

AAC is the only good codec for iPhone

SBC is the standard A2DP profile codec, and, of course, it is not the only one - there are also more advanced audio compression tools. And the most popular among them is the AAC (Advanced Audio Coding) codec. By the way, it is the best if you want to use wireless headphones with an iPhone, so if you have one, look for headphones that support it (and there are quite a few of them). And in general, the AAC format is used most of all by Apple - for example, all songs in iTunes or Apple Music use it.

Initially, AAC was developed as a successor to MP3 - it provides better sound quality at the same bitrate due to several optimizations: for example, frequencies that are not perceptible to humans are removed, redundancy in the encoded signal is removed, a wider window of 2048 pixels is used (you can read what windows are) and so on. So, in the end, this codec works significantly better than SBC and is quite suitable for everyday listening to music via Bluetooth - the main thing is that both the headphones and the device itself support it - otherwise the standard SBC codec will be used with dire consequences for the sound.

aptX is the optimal choice for lovers of good sound

This is one of the few codecs that can transmit audio over BT to MP3 and AAC without additional processing - and, therefore, without affecting the sound quality. Two-channel audio is transmitted here with a bitrate of up to 352 kb/s, and, of course, no frequencies are cut off: the frequency range from 10 Hz to 22 kHz is used, which is more than enough for the human ear.

In 2009, a more advanced version of aptX HD appeared; it allows you to transmit sound with a bitrate of up to 576 kb/s - and this is already enough to play some Hi-Res audio, which will clearly please music lovers.

However, alas, aptX has one rather serious problem: since this technology belongs to Qualcomm, it only works on devices with their Bluetooth chips, and that is why aptX support is not and cannot be on the iPhone, where there is Wi-Fi and BT responds with a chip from Broadcom. Well, as in the case of AAC, both the device itself and the headphones must support aptX - otherwise there will be a rollback to AAC or SBC.

LDAC is the only choice for music lovers

Music lovers, of course, will say - 576 kb/s in aptX HD is great, but there is music in flac with a bitrate twice as high. And here Sony comes to the rescue with its own codec, which provides audio transmission with a bit rate of as much as 990 kb/s with a sampling frequency of 96 kHz - which, in general, provides higher quality audio playback than from CDs. And if earlier this codec was used exclusively in devices from Sony, then starting with Android 8.0 it is included in the AOSP project, so if your smartphone has firmware on it, and you have headphones with LDAC support, then you can enjoy truly Hi- Res audio via Bluetooth.

Results

But in the end, we see that Bluetooth sound has developed so much that it will satisfy any wishes: for undemanding listeners with simple headphones and MP3 music with a bitrate of 128 kb/s, there is SBC. For those who are used to listening to music from iTunes or MP3 at 320 kb/s, there is AAC and aptX. Well, for music lovers with music in flac there is aptX HD and LDAC. However, do not forget - both devices must support the codec you need - otherwise you will listen to flac with the SBC codec, which you obviously will not like.