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What Bluetooth standards and audio codecs are worth knowing?
Bluetooth is a technology that has revolutionized the way we connect our devices wirelessly. With its development, various audio standards and codecs have emerged, which have a huge impact on sound quality and call performance.
Standard Bluetooth
Bluetooth is a short-range wireless technology standard used to exchange data between stationary and mobile devices over short distances and to create personal area networks (PANs). In the most commonly used mode, transmission power is limited to 2.5 milliwatts, giving a range of up to 10 meters (33 feet). This technology uses UHF radio waves in the ISM bands, from 2.402 GHz to 2.48 GHz.
Bluetooth is mainly used as an alternative to wired connections, enabling the exchange of files between nearby portable devices and the connection of mobile phones and music players with wireless headphones.
Version Bluetooth
| Version | Data transfer | Operating range | Compatibility | Power consumption | Failure rate |
|---|---|---|---|---|---|
| Bluetooth 1.0a / 1.0b | 732.2 kb/s | 10 m | - | Tall | High |
| Bluetooth 1.1 | 732.2 kb/s | 10 m | - | Tall | High |
| Bluetooth 1.2 | 1 Mb/s | 10 m | - | Tall | High |
| Bluetooth 2.0 + EDR** | 2.1 Mb/s | 10 m | any device with BT / possible interference | Tall | High |
| Bluetooth 2.1 + EDR** | 2.1 Mb/s | 10 m | any device with BT / possible interference | Tall | High |
| Bluetooth 3.0 + HS*** | 24 Mb/s | 10 m | any device with BT | Tall | High |
| Bluetooth 4.0 | 24 Mb/s | 10 m | any device with BT / BT 4.0 recommended | Mediocre | Moderate |
| Bluetooth 4.0 LE* | 1 Mb/s | 10 m | any device with BT / BT 4.0 LE recommended | Mediocre | Moderate |
| Bluetooth 4.0 + EDR** | 25 Mb/s | 10 m | any device with BT / BT 4.0 + EDR recommended | Mediocre | Moderate |
| Bluetooth 4.1 | 25 Mb/s | 10 m | any device with BT / BT 4.1 recommended | Mediocre | Moderate |
| Bluetooth 4.2 | 25 Mb/s | 10 m | any device with BT / BT 4.2 recommended | Mediocre | Moderate |
| Bluetooth 5.0 | 50 Mb/s | 10 m | any device with BT / BT 5.0 and newer recommended | Short | Slight |
| Bluetooth 5.0 LE* | 2 Mb/s | 10 m | any device with BT / BT 5.0 and newer recommended | Short | Slight |
| Bluetooth 5.1 | 50 Mb/s | 10 m | any device with BT / BT 5.0 and newer recommended | Short | Slight |
| Bluetooth 5.2 | 50 Mb/s | 10 m | any device with BT / BT 5.0 and newer recommended | Short | Slight |
| Bluetooth 5.3 | 50 Mb/s | 10 m | any device with BT / BT 5.0 and newer recommended | Short | Slight |
| Bluetooth 5.4 | 50 Mb/s | 10 m | any device with BT / BT 5.0 and newer recommended | Short | Slight |
*Bluetooth LE (Low Energy) - low energy consumption mainly in audio devices**Bluetooth EDR (Enhanced Data Rate) - increased data transfer***Bluetooth HS (High Speed) - increased data transfer
Bluetooth division into classes
| Class | Permissible power (mW) | Permissible power (dBm) | Maximum range (m) |
|---|---|---|---|
| 1 | 100 | 20 | 100 |
| 1.5 | 10 | 10 | 20 |
| 2 | 2.5 | 4 | 10 |
| 3 | 1 | 0 | 1 |
| 4 | 0.5 | -3 | 0.5 |
Class 1.5 - related to Class 1 BR/EDR (BR - Basic Rate) Class 2 - mainly used in mobile devices, cell phones, headphones with a range of up to 10 m
Audio codecs vs sound quality
SBC (Low Complexity Subband Coding) is the basic Bluetooth codec, built into the A2DP (Advanced Audio Distribution Profile) profile. A2DP has been around for about two decades and is free for manufacturers, so every Bluetooth device supports this codec.
SBC is widely supported and does not require much power from devices, but offers lower audio quality. It supports audio files up to 16 bit/48 kHz, with bit rates up to 345 kbps, although it is often limited to 256 kbps to save battery. To transmit 16-bit/48 kHz files losslessly, the bitrate would need to be four to six times higher.
AAC (Advanced Audio Coding) is the successor to MP3 and the default codec on iOS devices. It is more complex than SBC, which means higher power consumption, but also better sound quality. It supports 24-bit/44.1 kHz audio files, with bitrates up to 320 kbps, and is supported by Android (from version 8) and iOS devices.
Samsung Scalable Codec is used in the Galaxy Buds and can adjust the bitrate depending on the stability of the Bluetooth connection. The codec scales by analyzing the radio frequency environment and dynamically adjusting the bit rate (from 88 kbps to 512 kbps). When the Bluetooth connection weakens, the codec increases compression, lowering the bit rate, which prevents the connection from dropping at the expense of sound quality.
aptX is a codec from Qualcomm, created in the late 1980s, primarily for use in radio and movie studios. It is currently used for Bluetooth audio playback in many smartphones, tablets, Bluetooth speakers and AV receivers. aptX can transmit music at 16 bit/44.1 kHz, but it uses compression, so it is a lossy codec. It has a compression ratio of 4:1 and a bit rate of 352 kbps.
aptX HD is a newer version of aptX, released in 2016, offering better audio quality. Supports 24-bit/48 kHz audio files, with bitrate up to 576 kbps. It is supported by many headphones, such as Focal Bathys and the older Sony WH-1000XM3, but not the newer XM4 and XM5 models, which use Sony's LDAC codec. Most new devices support aptX Adaptive, which is an extension of aptX HD.
aptX Adaptive replaced aptX HD in 2018, combining the advantages of aptX HD audio quality and aptX Low Latency. By analyzing the number and intensity of radio frequencies in the environment, aptX Adaptive minimizes transmission interruptions and optimizes sound depending on whether you are on a phone call or listening to music.
aptX Adaptive dynamically adjusts bitrate in real time, scaling from 279 kbps to 420 kbps for high-resolution CDs and music. While these numbers may seem lower than aptX and aptX HD, aptX Adaptive is more efficient, providing better audio quality. It also supports 24-bit/96kHz files, being the first aptX codec with such capabilities. aptX Adaptive is backwards compatible with aptX HD on the transmitter side, which means a phone with aptX Adaptive can send audio to aptX HD headphones.
aptX Low Latency offers audio and video synchronization with a delay of less than 40 milliseconds when watching videos or playing games. It transmits music in 16-bit/44.1 kHz resolution at a bit rate of 352 kbps. It is currently less supported because it has been included in aptX Adaptive.
aptX Lossless is the latest aptX codec from Qualcomm. It supports 96 kHz audio with dynamic scaling of the bit rate from 279 kb/s to 860 kb/s, and its main feature is lossless CD-quality sound transmission (16-bit/44.1 kHz) in the classic Bluetooth standard and 48 kHz in the new Bluetooth LE (Low Energy) standard. To achieve this, the codec bitrate can scale from 1.1 Mbps to 1.2 Mbps. Qualcomm claims that "no data is lost when audio is encoded and decoded using aptX Lossless."
LDAC from Sony supports high-resolution audio up to 32-bit/96 kHz over Bluetooth at up to 990 kbps. According to Sony, LDAC allows for a three-fold increase in the amount of data streamed over Bluetooth thanks to more efficient encoding and "optimized packetization" of data.
LHDC (Low Latency and High Definition Audio Codec) was created by Savitech as an alternative to LDAC. Supports 24-bit/192 kHz audio quality at bitrates up to 1000 kbps. LHDC performs better in terms of low latency audio. While it has been promoted as the “next-generation standard for high-quality Bluetooth” and has been around for some time, its device support is still niche.
LC3 (Low Complexity Communications Codec) was introduced in 2020 as part of the Bluetooth LE Audio standard. It represents the next generation of Bluetooth audio technology, improving transmission efficiency. Supports 32-bit/48 kHz audio at 345 kbps. Thanks to greater power efficiency, LC3-enabled headphones should offer better battery life.
The first LC3-capable devices are already commercially available, but because both the source and receiver devices must support LC3, the technology is not yet widely used.
