Bluetooth is a wireless data transmission technology that enables communication between various mobile devices such as mobile phones, portable speakers, audio systems, laptops, printers, and digital cameras.
A Bluetooth module is a small chip containing a high-frequency transceiver (2.4 – 2.48 GHz) operating in the ISM (Industry, Science and Medicine) band. Initially, the communication range was limited to 10 meters, but with the emergence of special Bluetooth microcircuits on the market, this range increased to 100 meters. Thanks to radio technology, Bluetooth can overcome obstacles, allowing devices to remain connected even without a direct line of sight.
Bluetooth versions, profiles, and codecs
There are various Bluetooth versions, profiles, and codecs. For example, your device may be equipped with Bluetooth 3.0 and support the A2DP music profile, like many other Bluetooth devices over the years. Within the A2DP profile, different audio codecs can be used, such as MP3, AAC, SBC, aptX, LDAC, and others, to compress music files to bitrates suitable for Bluetooth transmission.
Bluetooth for audiophiles
It is important to note that having a Bluetooth transmitter does not guarantee the ability to use a device as a sound source for wireless audio equipment. Not all Bluetooth devices can provide distortion-free high-quality music playback or support high-bitrate and lossless formats (WAV, FLAC, MP4, APE).
A key aspect of music playback is the Bluetooth version and profile.
Modern devices typically support Bluetooth version 5.0 or higher. Most older models are 3.0 or 4.0. It is important to note that a purchased Bluetooth speaker may only support connection via protocol 2.1, which may limit connectivity capabilities. Although adapters are backward-compatible, their use may be restricted to a slower protocol. With each Bluetooth version update, device power consumption decreases, and starting from version 3.0, a second module was added for high-speed data transfer up to 24 Mbps.
For example, version 2.1 + EDR transmits data at no more than 2.1 Mbps, which is sufficient for MP3 playback. However, for audio-video streaming, it is recommended to use Bluetooth version 3.0 or higher.
Bluetooth profiles
Bluetooth profiles for music playback differ in specifications:
1. Headset Profile (HSP) provides wireless transmission of mono audio at a bitrate of 64 kbps, suitable for voice calls via a Bluetooth headset.
2. Hands-Free Profile (HFP) also transmits mono audio but with higher quality and support for MP3 and OGG formats.
3. Advanced Audio Distribution Profile (A2DP) is necessary for transmitting stereo audio. It not only handles audio streaming but also manages data compression before transmission. Before A2DP, there was a “voice layer” intended mainly for headsets with a bandwidth of only 64 kbps. The rest of the Bluetooth protocol consisted of the “data layer.” To improve sound quality, especially for stereo, the A2DP profile was developed, reallocating part of the available bitrate from the “data layer” to adapt it for music streaming.
4. Audio/Video Remote Control Profile (AVRCP) operates in parallel and enables control over playback device functions, including volume adjustment, track switching, and more.
Audio stream compression codecs
For high-quality music playback over A2DP, the choice of codec for compressing the audio stream is also important:
- Subband Coding (SBC) is the default codec in A2DP and can transmit audio at up to 328 kbps at 48 kHz. However, it compresses audio more aggressively than MP3, potentially degrading sound quality. SBC latency ranges from 170 to 270 ms.
- Advanced Audio Coding (AAC) is a more advanced codec using different compression algorithms, providing better sound quality compared to SBC.
AptX transmits MP3 and AAC files without additional transcoding, preserving audio quality. AptX latency is 120 ms. It exists in several versions for different audio streams: AptX 44.1 kHz, Enhanced AptX 48 kHz, AptX Lossless 96 kHz, and AptX Low Latency 48 kHz.
The main features of the last two versions are minimal playback delay and reduced CPU load during encoding. If lossless playback is not required and audio delay is not critical, the standard aptX version is sufficient, avoiding extra costs for supporting newer versions.
AptX HD is an improved version of aptX with light compression at 4:1 and a bitrate of 576 kbps, allowing transmission at a higher sampling rate and resolution up to 24-bit/48 kHz. This makes it especially suitable for high-resolution music requiring more data throughput.
LDAC is an audio coding technology developed by Sony for transmitting high-resolution (Hi-Res) audio over Bluetooth. The codec supports a sampling rate of 96 kHz and a bit depth of 24 bits. LDAC is a lossy codec using a hybrid encoding scheme for more efficient data compression and can transmit audio over Bluetooth at bitrates higher than aptX HD. It maintains the same 24-bit sampling rate as aptX HD but can reach up to 990 kbps, with lower modes of 660 kbps and 330 kbps.
How to enable LDAC on Android?
1. Open “Settings” and go to “About phone.”
2. Tap “Build number” seven times to unlock Developer options.
3. In the list of settings, open “Developer options.”
4. Select “Bluetooth audio codec.”
5. Choose LDAC from the available options.
With Bluetooth, any two devices will always operate at the lowest common version, using the simplest codec and protocol. Therefore, if one device does not support the required technology, you will not be able to fully enjoy high-quality audio.
For prolonged music listening, it is recommended to use Bluetooth version 3.0 or higher, the aptX codec, and the A2DP profile. For high-bitrate music playback, aptX Lossless support is required — other versions cannot provide the same quality due to compression during transmission.
Low Energy Bluetooth
Low Energy (LE) is a branch of the core Bluetooth technology aimed at lower power consumption. It is especially important for wearable gadgets, as it significantly affects their battery life.
Bluetooth LE is available alongside the classic version starting from Bluetooth 4.0. The standard is supported by all smartphones running iOS 5 and later, and Android 4.3 Jelly Bean and later.
Related sections:
Wi-Fi mode
Mobile devices