Monday, August 8, 2022

Bluetooth profiles and versions in headphones

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Bluetooth is a wireless technology for exchanging data over a short distance. Users are used to this feature, but what do we know about it, what are the differences between modern versions of Bluetooth, what profiles and codecs exist and how do they differ?

Bluetooth 1.2 (2003)
We skipped versions 1.0 and 1.1 because they offered rather primitive features and had deployment and compatibility issues. But version 1.2 was the first widely used Bluetooth technology. Adaptive frequency hopping (AFH) helped to avoid interference with Wi-Fi and other technologies at a similar frequency. Pairing speed has been improved.

Bluetooth 2.0 и 2.1 (2004)
Brand designation Bluetooth 2.0 + EDR. EDR technology is a profile that allowed for higher data transfer rates. In tandem with three-bit coding (versus one-bit), the speed increased from 1 to 3 Mbps (in practice, up to 2.1 Mbps). Interference handling has been improved and devices have started to consume less power. In version 2.1, device pairing (SSP) was added to make the connection faster and more secure.

Bluetooth 3 + HS (2009)
Brand name Bluetooth 3.0 + HS (High Speed). The new version made it possible to establish a Bluetooth connection using Wi-Fi frequencies, which made it possible to increase the transmission speed to 24 Mbps. But if the device did not have a Wi-Fi module, then the speed was limited to the same 3 Mbps as in the previous version of Bluetooth 2.

Bluetooth 4.0, 4.1, и 4.2 (2011–2014)
The advent of Low Energy technology in Bluetooth 4 has reduced power consumption for some peripherals, but not for wireless headphones. In the same version, each of the devices got the opportunity to simultaneously be both a hub and a client. This greatly expanded the functionality of portable technology, allowing the user, for example, to control some of the functions of his smartphone using headphones or smart watches.

There were no revolutionary changes in Bluetooth 4.1 compared to version 4.0. The developers have strengthened the protection against interference with the built-in range filter of LTE networks. As a result, a Bluetooth 4.1 device will look for another channel with less interference and a slightly different frequency. Also in the new version, both paired devices can be both master and slave. The maximum connection interruption time without losing pairing has increased from 30 seconds to 3 minutes.

Version 4.2 introduces new features for the Internet of Things. Each Bluetooth 4.2 enabled device has now been assigned a unique IP address.

Bluetooth 5.1 introduces the ability to determine the physical location of devices in a room down to a centimeter to provide a more reliable connection. Also, in the new version, devices pair faster due to improved caching. In 5.1, more channels were available for devices to connect, which reduced the amount of interference. This is useful when there are many Bluetooth devices in the same room.

Differences between Bluetooth 4.0 and 5.0 (2016)
Let’s look at the differences between these versions in more detail, because. there are several revolutionary changes here. There are more improvements in the new version of Bluetooth. They include:

increased by 4 times the actual range of distances from 50 to 200 meters (officially from 100 to 400 meters);
double increase in speed from 24 to 48 Mbps;
and an eightfold increase in throughput.
One of the key improvements in version 5.0 is the improved Low Energy technology, which previously had serious limitations on the use of wireless headphones. Now any audio devices equipped with a Bluetooth module can communicate with the source using Low Energy technology, which significantly reduces the power consumption of peripherals.

What is the difference between Bluetooth versions, profiles and codecs
So, we figured out the versions of the popular technology, which differ in speed, coverage area and additional features. But what are Bluetooth profiles and how do they affect headphones and other compatible devices?

Profiles define a set of features that a user gets when connecting devices via Bluetooth. For example, when choosing new headphones, you need to pay attention not only to the BT version, but also to the set of profiles, because. it directly affects the functionality of the audio device. To transmit an audio stream with maximum quality via Bluetooth, the A2DP profile is used, which will be discussed below.

Multimedia in modern devices is transmitted through a profile, but the most important thing is a codec that compresses the audio stream and transfers it to the headset with subsequent decoding. Under equal conditions, the sound quality depends on the type of codec used.

What are Bluetooth profiles
Now let’s take a closer look at the types of profiles. Bluetooth profiles are sets of instructions that define how Bluetooth devices work and implement functionality. There are about two dozen profiles for any device and purpose – from file transfer to wireless printing, but we are interested in those used in wireless headsets.

HSP – Provides basic headset performance with mic input, mono audio up to 64 kbps, and limited remote control – ringing, answering a call, ending a call, and volume control.

HFP is a more advanced version of HSP designed for mono hands-free headsets to answer calls without reaching for the phone. Supports some voice commands. Since the HFP 1.7 version, support for the mSBC codec has been added, support for the status of the headphone battery indicator.

AVRCP – provides remote control of multimedia playback: switching and rewinding the track, pause, start playback, adjust the volume. The AVRCP profile is for remote control only and is not used for audio streaming.

AVRCP Versions:

1.0 – remote control, including playback start, pause and stop.

1.3 – access to metadata and read the state of the media player:

state of the audio stream source (playing, stopping, etc.)
metadata with information about the artist, track name, etc.
1.4 – the ability to connect to multiple media players:

view status and manage multiple players;
view metadata for each media player, including playlist list
absolute volume control;
basic search capabilities.
1.5 – bug fixes for absolute volume control, viewing and other functions;

1.6 – view data and track information:

support for transferring covers through the BIP profile and the OBEX protocol;
the number of items in the player’s folder without loading the playlist.
AVRCP 1.6 is supported by all Android devices starting from version 8.0.

A2DP – Designed to transmit multimedia and stereo audio over Bluetooth, providing much better audio quality compared to HSP / HFP. By itself, it does not allow remote control of playback functions, therefore it is most often used in conjunction with AVRCP.

A2DP Versions:

1.2 – expansion of the list of supported codecs.

1.3 – All of 1.2 plus streaming latency reduction to improve A/V sync, plus:

added interoperability with new Bluetooth profiles, improved security and standby;
expanded list of supported codecs.
Thus, in order to listen to an audio stream with high-quality stereo sound and control playback functions, you need a headset and a transmitting device (host) that supports both AVRCP and A2DP profiles at the same time.

Let’s also look at secondary profiles that offer additional features.

PBAP – Used to access the phone’s phone book using a wireless headset. In practice, this allows the headset to speak the name of the person who is calling, as well as voice commands to access the phone book for dialing.

SPP is a profile that defines how two devices will communicate, emulating a wired connection like USB or RS-232.

DID – Identifies the device class, manufacturer, and model. For example, this makes it possible to see the full model name of the connected headset on the phone screen.

ICP – Support for voice calls between compatible Bluetooth devices.

SDAP – The profile is used by applications to discover services that may be available to specific Bluetooth connected devices. For example, an SDAP audio streaming application can check if a given headphone model supports the aptX HD codec. Another example would be access to premium content when using certain models of headphones, or, conversely, blocking access for certain models of headsets due to copyright compliance with digital content.

What are Bluetooth codecs
The sound quality under equal conditions depends on the maximum bitrate and encoding algorithms. For these purposes, different codecs are used. In the bar graph below, you can see how the bitrates of the most popular Bluetooth codecs vary. It is worth noting that the codec must be supported by both the transmitting and receiving device.

Bitrate of popular Bluetooth codecs

SBC is at the bottom of the list among the most popular Bluetooth codecs. However, it is integral to all A2DP-enabled devices, making it almost universal.

SBC provides a low load on the mobile processor, but this is achieved through aggressive processing and reduced frequency range. As a result, there is a significant loss of data in the original audio file, which is especially noticeable at high frequencies with the appearance of background noise.

AptX, aptX LL, aptX HD, и aptX Adaptive от Qualcomm

A major manufacturer of mobile processors, Qualcomm promotes its own codecs by building their support into proprietary processors. Codecs differ in bandwidth, and as a result, in the sound quality they provide. But in general, the entire AptX line shows decent sound, and AptX HD is called by many users the “gold standard”.

AptX offers a slightly higher bitrate than the standard SBC, but delivers a head-to-head sound with different algorithms, not as aggressively cutting high frequencies. Although such an algorithm requires more computing power, which increases the load on the processor, modern devices have enough performance headroom to work with the entire AptX line.

AptX HD makes it possible to hear significantly less background noise and hear almost every element of the musical composition. This is achieved by either lossless audio coding or minimal loss, which is due to the limitations of the Bluetooth standard.

AptX LL ensures the lowest latency in audio transmission. In order for the human brain not to notice the audio lagging behind the video, it is necessary that the delay in the transmission of the audio stream be no more than 40 ms . AptX LL with minimal latency allows you to watch content and play games without sound lag.

AptX Adaptive sits between AptX HD and AptX in terms of audio quality. At the same time, it approaches AptX LL in terms of latency – 40-80 ms. The codec has a variable bitrate of 279–420 kB/s, which adapts to the quality of the files being played.

LDAC от Sony

LDAC. Sony offered its own codec so as not to lose the battle for music lovers. LDAC has three modes of operation that allow streaming at bit rates up to 990 kbps. But the quality-priority mode is supported by a fairly modest number of devices. There are some stability issues in the highest bitrate mode. And the first two modes of 660 kbps and 330 kbps are not superior in quality to the AptX codecs.

AAC

A popular codec used by many music streaming services, including iTunes. The maximum bitrate is 256 kbps. The main objective of this codec was to surpass the quality of SBC and the capabilities of the MP3 format. Due to more complex processing algorithms, AAC does retain more musical information compared to a standard codec.

The codec is slightly different when working on Android and iOS devices. On Android, it’s called Fraunhofer FDK AAC, and on iOS and Mac devices, it’s called Apple AAC.

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