In - Depth Analysis of Sound Quality in Bluetooth Audio Devices: Codecs, Chips, and Underlying Technologies

Since the advent of Bluetooth headphones in 1999, the sound quality of Bluetooth audio devices has been a topic of great concern. In the early days, due to the limited bandwidth of Bluetooth, the label "just for basic sound" was attached to them.

In 2008, with the popularization of the Bluetooth A2DP protocol, consumer - grade Bluetooth audio devices emerged, and sound quality gradually became a key promotional point for manufacturers.

When new products are launched, "sound quality improvement" is often mentioned, and parameters such as Bluetooth audio codecs like SBC, AAC, AptX, LDAC, LHDC/HWA are crucial.

However, different devices use various formats, leaving people wondering about the advantages and disadvantages of these formats and their impact on sound quality.

Below, we will deeply explore these codecs and other factors affecting the sound quality of Bluetooth audio devices.

Codecs: The Key to Sound Quality Breakthrough

Currently, the Bluetooth bandwidth supports a maximum transmission speed of 48Mbps, and up to 2Mbps in low - power mode.

Theoretically, only 1.4Mbps of bandwidth is required to achieve CD - quality sound. However, the Bluetooth A2DP transmission protocol stipulates that the maximum audio standard is 328kbps for mono and 512kbps for stereo, forcing high - format audio files to be decoded and compressed before transmission.

For example, an MP3 audio file needs to go through two decoding and one encoding processes from the transmitting end to the headphones (MP3→PCM→audio decoding→PCM).

To improve sound quality, the Bluetooth protocol and audio manufacturers have introduced various codec formats without changing the A2DP protocol.

Before understanding codec technologies, several key parameters need to be clarified:

• Sampling Rate: It refers to the frequency of sampling an analog signal, with the unit of Hz, representing the number of samples per second.

• Sampling Bit Depth (Bitwidth): It is used to measure the precision of collecting an analog signal, with the unit of "bit". The higher the value, the higher the precision.

• Bitrate: It reflects the data rate, with the unit of kbps (kilobits per second). Under the same encoding, the higher the bitrate, the better the quality, but it also requires a higher bandwidth.

For example, 44.1kHz/16bit/328kbps represents the sampling rate, sampling bit depth, and bitrate respectively. The higher the values, the better the transmission quality.

SBC (Sub - band coding): The Official Basic Codec of Bluetooth

SBC is the codec format mandatory in the A2DP protocol, supported by all Bluetooth devices.

It has a relatively low encoding complexity and a moderate compression ratio, but the sound quality is slightly poor at the same bitrate. It supports sampling rates of 16kHz, 32kHz, 44.1kHz, and 48kHz, with a data transmission rate of 328kbps.

Its advantage is high universality, while the disadvantage is poor sound quality and high latency, ranging from 170ms to 270ms.

AAC: Advanced Audio Coding, Apple's Favorite

AAC stands for Advanced Audio Coding. It emerged in 1997 and was initially based on the MPEG - 2 audio coding technology. It was jointly developed by several companies to replace the MP3 format.

It has more sampling rate options (from 8 KHz to 96 KHz) and a higher upper limit of the number of channels (48 channels, while MP3 has a maximum of stereo in MPEG - 1 mode and 5.1 channels in MPEG - 2 mode).

The commonly used bitrate of AAC in Bluetooth is 256Kbps. When using an AAC audio source, Bluetooth needs to first decode it into PCM and then encode it into the AAC encoding supported by Bluetooth for transmission.

Apple has a particular preference for AAC. Devices such as iPhones, iPads, and AirPods support AAC, and many music files in the iTunes software are also stored in the AAC encoding format. Its latency is better than that of SBC, ranging from 90ms to 150ms.

aptX: Five Technologies for Sound Quality Enhancement

aptX was originally named apt - X. It was acquired and renamed by CSR in 2010, and CSR was then acquired by Qualcomm in 2015. Currently, aptX includes five technologies:

• aptX: It adopts a high - performance lossless compression algorithm, supports 48kHz/16 - bit LPCM audio data, creating CD - quality high - quality sound. The data transmission rate is 352kbps, and the latency is 100 - 200ms.

• aptX HD: It achieves 24 - bit high - definition sound quality via Bluetooth, supports 48kHz/24 - bit LPCM audio data. The increase in sampling rate brings a lower signal - to - noise ratio and significantly reduces distortion. It allows you to hear the slightest details in music, providing a realistic sound quality. The data transmission rate is 576kbps, and the latency is about 200ms.

• aptX Low Latency: It achieves high - quality sound and low latency. It supports 16 - bit/44.1KHz audio with a latency of less than 40ms, enabling synchronization of movie and game audio.

• aptX adaptive: It supports a maximum sampling rate of 96kHz/24bit, belongs to the Qualcomm Snapdragon Sound technology. It has two working modes: default and low - latency. It can dynamically adjust between 276 - 420kbps, with the latency controlled between 50 - 80ms.

• aptX Lossless: Qualcomm's latest audio technology, with a maximum sampling rate of up to 96kHz/24bit and a bitrate increased to a maximum of 1000kbps, supporting "lossless sound quality".

LDAC: Sony's High - End Codec Technology

The LDAC codec technology developed by Sony can achieve a maximum bitrate of 990kbs and supports up to 48kHz/96bit, that is, Hi - Res Audio.

It provides three transmission modes: the 990kbps mode with quality priority, the default 660kbps standard mode, and the 330kbps mode similar to the ordinary Bluetooth standard.

Although LDAC can provide high - quality audio, its stability is poor. When the signal is poor or interfered with, it will reduce to a bitrate of 660Kbps or 330Kbps for communication to ensure connectivity.

The good news is that most Android devices now support it, but the Bluetooth audio device also needs to support the LDAC encoding format. At the same time, LDAC is the first codec format to obtain the Hi - Res Audio Wireless certification.

The certification standard requires the analog audio frequency response to reach above 40 KHz and the digital audio sampling rate to reach above 96KHz/24 bit.

LHDC: The New - Generation High - Quality Bluetooth Encoding Solution

LHDC, short for Low - Latency Hi - Definition Audio Codec, was developed by the Taiwanese manufacturer Savitech. Similar to LDAC, it supports high - resolution audio, can transmit 24bit/96kHz/900kbs audio, and has obtained the Hi - Res Audio Wireless certification.

LHDC supports bitrates of 400/560/900 kbps depending on the stability of the Bluetooth signal. There is also a low - latency version, LHDC LL, with a latency of about 30ms, which can be experienced on Android devices.

In 2022, driven by Bluetooth LE Audio, the new LHDC - V codec was released, supporting 24bit/192Khz transmission and a frequency response range of 20Hz - 96Khz, comprehensively improving the sound quality experience.

HWA: China's Audio Standard

HWA has two meanings: one is the High - Definition Audio Wireless Transmission Standard and Industry Alliance established in 2018, and the other is the HWA High - Definition Wireless Audio Standard (Hi - Res Wireless Audio) released in 2022.

The HWA Alliance was led by Huawei and the China Audio Association, and the technical leader is Savitech, the Taiwanese manufacturer that developed LHDC.

In July 2022, multiple companies jointly released the HWA High - Definition Wireless Audio Standard.

It is a certification standard based on the LHDC audio encoding technology, not a Bluetooth audio encoding. It provides three bitrate modes: 400kbps/500kbps/560kbps and 900kbps, with the same nature as the Hi - Res Audio Wireless standard led by the Japanese Audio Society (JAS).

Huawei also independently developed the L2HC audio codec technology, which can achieve an audio transmission bitrate of up to 960Kbps, close to LDAC's 990kbps, and has a more flexible bitrate space. Similar to aptX adaptive, it can adapt to lower bitrates in some interference - prone scenarios.

LC3: The New Hope for the Future of Bluetooth

The Bluetooth 5.2 protocol update introduced LE audio, and LC3 is a new high - quality, low - power audio codec in this communication protocol.

It can encode voice and music at various bit - rates and can be added to any Bluetooth audio profile. Thanks to its low complexity and relatively low frame duration, it can achieve lower Bluetooth transmission latency. Compared with the SBC encoder, even if the LC3 bitrate is reduced by 50%, it can still ensure good sound quality.

It also supports multiple bit - depths (16/24/32bit) and sampling rates (8kHz, 16kHz, 24kHz, 32kHz, 44.1kHz, and 48kHz), and the bitrate supports 64kbs, 96kbs, 128kbs, 192kbs, and 248kbs.

Although its supported parameters are not as high as those of LDAC and LHAC, its stability and low - power consumption are much better.

With the development of Bluetooth technology, audio codecs are constantly evolving.

As long as the audio transmission protocols of the mobile phone and the Bluetooth audio device match, users can experience high - fidelity or even lossless sound quality. Android devices support a more comprehensive range of audio codecs. Although Apple mainly uses AAC at present, it is expected to cover more types in the future.

Bluetooth Chips: The Hardware Foundation of Sound Quality

In addition to codecs, Bluetooth chips have a significant impact on sound quality, similar to the SOC of a mobile phone.

In the market, there are high - end self - developed chips such as Apple's W1/H1 chips, Huawei's Kirin A1 chips, and Qualcomm's high - performance QCC series chips, as well as cost - effective chips represented by Zhongke Lanxun, Realtek, and JieLi.

Good chips offer stronger stability and better compatibility with a wider range of audio codecs, providing a hardware guarantee for sound quality.

In conclusion, the sound quality of Bluetooth audio devices is constantly improving. With the update of Bluetooth versions and the popularization of LE audio scenarios, the usage scenarios of Bluetooth audio devices will become more diverse.

The improvement of audio codec sampling rates will gradually promote the arrival of the "lossless" sound quality era, eliminating the misunderstanding that "wireless cannot have good sound quality".

So, do you prefer to embrace the "new wireless era" or stick to the "wired camp"?

Tags: #BluetoothAudioDevices #SoundQuality #BluetoothCodecs #BluetoothChips #AudioTechnology