Mobile phone with bluetooth a2dp. Bluetooth Headset, HandsFree, A2DP, AVRCP, HSP, EDR and other Bluetooth profiles of mobile devices. Advanced Audio Coding: Advanced But Not Perfect

In the century modern technologies You won't surprise anyone with wireless devices: we actively use Wi-Fi on phones and laptops, we connect to computers wireless mice and keyboards, and listen to music through Bluetooth headphones. And here a snag happens - how to choose the best headphones specifically for your devices, because there are a lot of BT audio transmission protocols, and not all of them are supported by both the headphones and the device itself?

History and characteristics of the Bluetooth standard

But we'll start, as usual, in the history of BT. And they began to create it, which is remarkable, a few years before USB - back in 1994, Ericsson, a fairly well-known manufacturer of telecommunications equipment, began to work on this standard. The standard itself was developed as a wireless alternative to a wired RS-232 connection (better known as a serial port). The specifications themselves were already 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, recall, is included in the IEEE 802.11 standard). Currently, the Bluetooth SIG group includes more than 18,000 companies, making Bluetooth one of the few major standards for short-distance data transmission.

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, the use of one range leads to interference (overlap) of signals - and this, in turn, negatively affects the stability and speed of work. Taking into account the fact that the sound must always be transmitted in the same quality without delays, the developers of the standard went for a trick. Perhaps the most the main problem for BT, it is Wi-Fi - there are many such networks in the 2.4 GHz band in every home, and in total in this range there can be 13 channels with a width of 22 MHz:


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


This is done specifically in order to greatly reduce the likelihood of signal overlap in such a small frequency range. But this does not cancel the interference - small BT channels may well get 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 the large Wi-Fi channel are ignored:


So if you use Bluetooth in one place, then in theory there are no problems with sound transmission - out of 79 channels, free ones will be selected, which will provide sufficient speed. If you move, then there may be problems - but, on the other hand, often you saw on the street Wi-Fi networks? So the technology of sound transmission over BT can be considered quite noise-resistant, and it remains only to deal with the standards for sound transmission over it.

Bluetooth profiles for audio transmission

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

The next profile was called HFP (Hands-Free Profile), and, as the name implies, it was again intended for headsets - all the same mono sound with low quality. Of the improvements - more advanced work: for example, when making a call, it was possible to transmit sound from the phone to the speakers of the car, and use the microphone in the car to answer. But we are interested in exactly the transfer of music, and for her this profile, for obvious reasons, is categorically inappropriate.

The first profile designed specifically for the transmission of stereo sound was A2DP - Advanced Audio Distribution Profile. It was in it that the function of polling the headphones connected to the device appeared in order to find a common codec for them, and, most importantly, it was in this profile that the ability to control audio compression appeared: alas, compression cannot be avoided due to low bandwidth Bluetooth, but the compression itself is highly dependent on the codecs used and the BT version, so the final sound 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 principle of encoding itself is similar to MP3, but here the emphasis is not on minimizing audio losses, but on simplifying computations, so that even on weak mobile processors, compression occurs very quickly. Therefore, for example, frequencies above 14 kHz are completely cut off. Therefore, although SBC allows bit rates up to 345 kb / s, MP3 at 320 kb / s will sound much better - just look at the spectra:


As you can see, the best sound is conveyed by AptX (about it below), then MP3 comes, and SBC is in last place.

AAC is the only good codec for iPhone

SBC is the standard A2DP profile codec, and of course it is far from the only one - there are also more advanced audio compression tools. And the most popular among them is the AAC (Advanced Audio Coding) codec. It is, by the way, the best one if you want to use wireless headphones with your iPhone, so if you have it, look for headphones with its support (and there are quite a few of them). And in general, the AAC format is used most of all in Apple - for example, all songs in iTunes or Apple Music use it.

AAC was originally designed as the successor to MP3 - it gives best quality sound at the same bitrate due to several optimizations: for example, frequencies that are not perceived by humans are removed, redundancy in the encoded signal is removed, a wider window of 2048 points is used (that such windows can be read), and so on. So, in the end, such a codec works much better than SBC and is quite suitable for everyday listening to music via Bluetooth - the main thing is that both headphones and the device itself support it - otherwise the standard SBC codec will be used with sad consequences for sound.

aptX is the best choice for amateurs good sound

This is one of the few codecs that can transmit audio in MP3 and AAC via BT 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: it is used frequency range from 10 Hz to 22 kHz, 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 obviously be pleased with 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 there is no and cannot be aptX support on the iPhone, where Wi-Fi is and BT is responding with a chip from Broadcom. Well, as in the case of AAC - both the device itself and the headphones must support aptX - otherwise, it will rollback to AAC or SBC.

LDAC is the only choice for music lovers

Music lovers, of course, will say - 576 kb / s for aptX HD is great, but there is music in flac with a bitrate and 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 rate of 96 kHz - which, in general, provides better audio reproduction than from CDs. And if earlier this codec was used exclusively in devices from Sony, then starting from 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 really enjoy Hi- Res-audio over Bluetooth.

Outcomes

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

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

Usually from brief description mobile device, you can only find the name wireless interfaces with which it is equipped. In the detailed specification, as a rule, there is additional information, in particular the versions of the wireless interfaces (for example, Wi-Fi 802.11b / g / n and Bluetooth 2.1). However, this is far from always enough to fully assess the capabilities of wireless communications of the device in question. For example, to understand whether a particular peripheral device connected via Bluetooth will work with a smartphone or tablet at your disposal.

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

Scope of application

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

The introduction of Bluetooth into consumer devices for the mass market began in the first half of the past decade. Currently embedded Bluetooth adapters are equipped with many models of laptop PCs and mobile devices. In addition, a wide range of peripheral devices (wireless headsets, keypads, keyboards, speaker systems, etc.) equipped with this interface is 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 (inside the same house, room, vehicle, etc.) desktop and laptop PCs, peripheral and mobile devices and NS.

The main advantages of Bluetooth in comparison with competing solutions are low power consumption and low cost of transceivers, which allows it to be embedded even in small devices with miniature batteries. In addition, OEMs are exempted from paying royalties for installing Bluetooth transceivers in their products.

Connecting devices

Through 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 defines the template that will be used by all slaves, and also synchronizes their work. The devices connected in this way form a piconet. Within one piconet, one master and up to seven slaves can be combined (Fig. 1 and 2). In addition, the presence of additional slaves in the piconet (over seven), which have the status of parked (parked): they do not participate in the exchange of data, but are in synchronization with the master.

Rice. 1. Diagram of a piconet,
combining two devices

Rice. 2. Diagram of the piconet,
combining several devices

Several piconets can be combined into a distributed network (scatternet). For this, a device operating as a slave in one piconet must perform the functions of a master in another (Fig. 3). Piconets included in one distributed network are not in sync with each other and use different templates.

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

The maximum number of piconets in a distributed network cannot exceed ten. Thus, a distributed network allows for a total of 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 via Bluetooth at the same time.

Radius of action

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

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

Bluetooth versions and their differences

The first version of the specification (Bluetooth 1.0) was approved in 1999. Soon after the interim specification (Bluetooth 1.0B), Bluetooth 1.1 was approved - it fixes bugs and eliminates many of the shortcomings of the first version.

In 2003, the basic Bluetooth 1.2 specification was approved. One of its key innovations was the introduction of the adaptive reconfiguration method. operating frequency(Adaptive frequency-hopping spread spectrum, AFH), thanks to which the wireless connection has become much more resistant to electromagnetic interference. It also reduced the time it took to find and connect devices.

Another important improvement in version 1.2 was an increase in the data exchange rate up 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 kbps one way and 57.6 kbps the other.

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

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

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

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

In 2007, the basic Bluetooth specification 2.1 + EDR was approved. One of the innovations implemented in it was the energy-saving Sniff Subrating technology, which made it possible to significantly (from three to ten times) increase the duration autonomous work mobile devices. Also, the procedure for establishing a connection between two devices has been greatly simplified.

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

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

The basic Bluetooth 4.0 specification was approved in June 2010. The key feature of this version is the use of data transmission technology with low power consumption(low energy technology). Reducing 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 work constantly, but is turned on only for the duration of the data exchange. Contrary to popular belief, Bluetooth 4.0 does not provide faster data transfer rates than Bluetooth version 3.0 + HS.

Bluetooth profiles

The interoperability of devices when connected via Bluetooth is largely determined by the set of profiles that each of them supports. This or that profile provides support for certain functions, for example, transferring files or streaming media, providing network connection etc. For information on some of the Bluetooth profiles, see the sidebar.

It is important to understand that using a Bluetooth connection to perform a task is only possible if the corresponding profile is supported by both the master and the slave device. 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 profile (Object Push Profile). And, for example, to use a mobile phone as a wireless cellular modem, this device and the connected computer must support the Dial-up Networking Profile (DUN).

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

Thus, the set of supported profiles is an important factor that must be taken into account when evaluating the capabilities of a particular device. Unfortunately, some models of mobile devices support minimal set profiles (for example, only A2DP and HSP), which significantly limits the possibilities wireless connection 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, in some devices the ability to transfer files is blocked certain formats(images, videos, electronic books, apps, etc.) under the pretext of fighting piracy. True, in fact, it is not lovers of counterfeit media content that suffer from such restrictions and software, and honest users, even forced to transfer photographs taken by the built-in camera with their own hands to a PC in a roundabout way (for example, by sending required files on own address Email).

Bluetooth profiles A2DP(Advanced Audio Distribution Profile) - provides two-channel (stereo) audio stream transmission 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 can be used or another one defined by the device manufacturer. AVRCP(Audio / Video Remote control Profile) - allows you to manage standard functions TVs, home theater systems, etc. A device supporting the AVRCP profile is capable of performing the functions of 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 the transmitted images, taking into account the specifics of the 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 on a printer. An important feature of the BPP profile is that on the device from which the object is sent for printing, there is no need to install a specific driver for the existing printer model. DUN(Dial-up Networking Profile) - connects 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 fax module) to receive and send fax messages from your PC. FTP(File Transfer Profile) - Provides file transfer as well as access to file system connected device. The standard set of commands allows you to navigate the hierarchical structure of the logical drive of the connected device, as well as copy and delete files. GAVDP(General Audio / Video Distribution Profile) - provides transmission of audio and video streams from a signal source to a playback device. It is the base for A2DP and VDP profiles. HFP(Hands-Free Profile) - Provides connection automotive devices hands-free to mobile phone for voice communication. HID(Human Interface Device Profile) - describes the 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 mobile phones and PDAs, which allows them to be used as wireless remotes for control graphical interface OS or separate applications on the PC. HSP(Headset Profile) - allows you to connect wireless headset to a mobile phone or other device. In addition to audio streaming, functions such as dialing, answering an incoming call, ending a call and adjusting the volume are provided. OPP(Object Push Profile) - basic profile for sending objects (images, business cards, etc.). For example, you can transfer a contact list from one mobile phone to another, or a photo from a smartphone to a PC. Unlike FTP, OPP does not provide access to the attached device's file system. PAN(Personal Area Networking Profile) - allows you to combine two or several devices in local area network... In this way, you can connect several PCs to one with Internet access. Besides, this profile provides remote access to the PC acting as the master. SYNC(Synchronization Profile) - used in conjunction with the basic GOEP profile and synchronizes personal data (diary, contact list, etc.) between two devices (for example, a desktop PC and a mobile phone).

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

First, you need to take into account the specifics of your existing fleet of Bluetooth devices. After all, as already mentioned, maximum speed data transmission is determined by a device equipped with the most old version interface. In addition, not all tasks require high data transfer rates. If this is really an important factor for copying media files (sound recordings, images) or broadcasting an audio stream with a low compression ratio, then for the normal interaction of the phone with wireless headset or to exchange contacts with another device, Bluetooth 2.0 capabilities will be enough.

Second, in many cases a much more important factor than the maximum wireless speed 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 able to interact. Unfortunately, this information is rarely given even in the complete specification of the device, and it is often necessary to search for it in the text of the user manual or in user forums.

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

Modern smartphones have the standard wireless transmission A2DP Bluetooth information. It is designed to distribute audio over a radio channel to peripherals... A mobile phone acts as a transmitter, and a wireless headphone or portable speaker acts as a receiver. A2DP Bluetooth technology eliminates wires that get in the way of portable audio.

The main feature of the A2DP Bluetooth profile is low bandwidth, so the smartphone is forced to process the track in a special way to reduce the size before transmitting sound. 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. Also, the user is able to control the playback of tracks through the keys located on the case of peripheral devices.

1. To start using the A2DP Bluetooth connection, you must 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 must be charged and displayed in the list of devices available for connection. Here you just need to select the desired headset and wait for the smartphone to sync.
3. After the described actions, you can use all the possibilities wireless headphone- 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 earphones close to the phone. If you move some distance away, the sound will be interrupted or noisy.

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.

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

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

Initially, the "blue tooth" had a lot of problems with the speed and reliability of communication, power 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.

Several improvements - for example, the simplification of the "pairing" procedure in version 2.1 and a significant reduction in the load on the batteries in the current version 4.0 - made daily life music lovers are much more comfortable. Even more comfort was made by the emergence of NFC technology - in conjunction with it, Bluetooth does not require any ceremony at all in the mutual recognition of the receiver and transmitter, it is enough just to touch the gadgets to each other. But in general, progress 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. And actually how?

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 2.4 GHz region - Wi-Fi routers, wireless computer keyboards and mice, some DECT phones and a lot of other equipment.

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

Curiously, the Bluetooth logo consists of two Scandinavian runes: "haglaz" and "berkana" (analogs of the Latin letters H and B)

On the other hand, it is multifunctional. 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. Not surprisingly, Bluetooth has so many different so-called. "Profiles", each of which provides the performance of a particular task, defining the technical parameters of the interaction between the Bluetooth transmitter and the receiver. The total number of profiles is measured in dozens (according to the article on Wikipedia, there are 35 basic ones), only three are responsible for sound transmission. How do they differ from each other?

Bluetooth profiles HSP, HFP and A2DP

The first of the Bluetooth audio profiles is called HSP - Headset Profile. As the name implies, it was created 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 of 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 destination is all the same mono 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 came along, many hi-fi manufacturers took notice of it. But before everyone else, there were small companies that made adapters, like the one shown in the photo GOgroove BlueGate - a small box with a DAC and 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 audio source to find mutual language with wireless acoustics, and most importantly - controls the audio compression for sending over the "blue-tooth" channel. This procedure cannot be avoided due to the low bandwidth of Bluetooth, but the compression level used for compression algorithms and, ultimately, the loss in sound quality can vary significantly. Here, as they say, the nuances arise.

SBC codec squeezes coarser than MP3

As you know, you can compress sound in different ways. Lossy or lossy, low or high bitrate, with different settings, using different codecs. Instead of any of the ubiquitous codecs for compressing audio streams, the A2DP profile uses its own compression algorithm Subband Coding - or, simply, SBC - by default.

A comparison by Brent Buttervoot (author of About.com) shows the difference in noise generated when a 5, 10, 12.5 and 20 kHz tone is applied. 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 arranged in a slightly different way: the main task is not so much to minimize audio losses as to simplify calculations. Everything should be fast, simple and easily doable even for the most flimsy mobile processor.

As a result, SBC dispenses with sound without further ado - for example, frequencies above 14 kHz are simply cut off during conversion, as a result of which the frequency range is noticeably narrowed. Not surprisingly, even with an equal bitrate with MP3 (and SBC allows bitrate up to 320 kB / s), SBC-encoded audio sounds noticeably worse.

This graph shows the spectra when broadcasting a 1 kHz signal through aptX (blue) and SBC (green), and 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 ordinary mp3 files - after all, during wireless transportation, they are first decoded and then compressed again, this time much coarser. Fortunately, SBC is the primary, but not necessarily the only, audio 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 humble musical ability, is not best remedy to draw the attention of music lovers to Bluetooth technology. That is why the developers of many "blue-tooth" 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 only familiar to those who like to delve deeper into technical specifications Bluetooth, abbreviation AAC, is well known to the general public. Still would! After all, this is the format used, for example, in iTunes. The initial task of the algorithm developers was to surpass MP3 in sound quality at the same bit rates - it is no coincidence that its name stands for Advanced Audio Coding, "advanced audio coding."

Due to more complex algorithms, AAC really saves more musical information than mp3, and even more so SBC. Not surprisingly, its inclusion in the set of codecs supported by the A2DP profile noticeably improves the sound of Bluetooth speakers and headphones.

The main thing is to make sure that the AAC codec is supported by both "blue-tooth" devices: the one that serves as the transmitter of the audio signal, and the one that works on its reception. If of a pair of such devices, AAC encoding can only understand one thing - the A2DP profile automatically rolls back to the base codec. With obvious sound implications.

AptX codec: the best option for the music lover

Even more advanced audio compression is provided by the aptX codec, which CSR is actively promoting in the wireless Bluetooth audio market. Its creators are promoting it as a "CD-quality" music streaming medium.

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

In fact, this is not entirely true, although the algorithms that underlie aptX, by the principle of their work, really resemble lossless encoders, which compress the audio stream without losing audio information. Among the advantages of aptX is the ability to Bluetooth-broadcast MP3 and AAC without additional processing, and therefore without degrading the sound.

A special version of aptX Low Latency, tailored for the needs of gamers and moviegoers, also provides a minimum delay in signal delivery - which means watching a movie without lagging behind the lines of 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 quite solid 10 Hz - 22 kHz, but the high complexity of the algorithms used requires mobile processors 3x the processing power of the base 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, it is not necessary to lay out so much cash: in the catalogs of Samsung, Sony, HTS and Asus there are many models with support for an advanced codec, including quite affordable ones.

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

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

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 speak and control your phone without using your hands. Most commonly used in cars. In fact, these are devices that provide the ability to conduct a conversation without holding a mobile phone, communicator in hand. Consists of earphone and 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 that allow you to control the player of your mobile device.

The wireless headset connects to your mobile device using. It is able to pick up a mobile phone signal at a distance of up to 10 m.

For some time now, Bluetooth wireless technology has been indispensable for equipping mobile phones with various external devices such as handsfree, external memory or wireless modems. V recent times become more and more popular Bluetooth headsets and headphones (). Some of them have the opportunity to work not only with mobile phones and PDA, but also with other devices that do not have a protocol Stereo bluetooth through adapters.

The emergence of phones that support the ability to use wireless bluetooth stereo headphones for listening to music, allowed their owners to feel the real joy of the complete absence of wires. However, the cost of such phones and the Bluetooth headphones themselves does not allow us to speak about the massive nature of this phenomenon.

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