When you listen to music via Bluetooth, the quality isn’t always up to scratch. This is partly due to the audio codec used, in other words the software that compresses and decompresses the sound during wireless transmission. This is where aptX comes in, a codec designed to offer far better sound reproduction than the basic standard used by all devices, SBC.
Why compress Bluetooth sound?
Bluetooth has limited bandwidth: it can’t transmit as much data as a conventional audio cable. To fit music into this “pipe”, it is compressed. The SBC codec does this in a simple way, but with fairly aggressive compression, which can lead to loss of detail, reduced dynamics, and even latency between sound and image in videos.
What is the aptX codec?
aptX is an audio codec first developed in the 1980s, then acquired by Qualcomm. It was designed to reduce the loss of sound quality associated with compression, while remaining compatible with the classic Bluetooth standard. The idea is to offer quality closer to that of an audio CD, without the need for a cable.
In concrete terms, aptX uses a more efficient compression method than SBC, with an average bit rate of 384 kbps (compared to 192 to 345 kbps for SBC), which means that the sonic detail of a compressed audio file (such as MP3) or even an uncompressed file (such as FLAC or PCM) is better preserved.
What variants of aptX are there?
- Classic aptX: the most common, compatible with many Android devices. It improves sound quality compared to SBC, with latency reduced to around 120-150ms.
- aptX HD: for higher-quality audio files (up to 24-bit/48kHz), with bit rates of up to 576 kbps. Ideal for wireless Hi-Fi enthusiasts.
- aptX Low Latency: designed for games and videos, with latency reduced to around 40ms to avoid lags between the picture and the sound.
- aptX Adaptive: automatically adjusts throughput according to network conditions to balance quality and stability, while offering reasonable latency (between 50 and 80ms).
- aptX Lossless: the latest version, which aims for lossless quality, with a bit rate of up to 1 Mbps, similar to or even higher than that of a CD.
How to benefit from the aptX codec
Both devices need to be compatible: the transmitter (such as a smartphone) and the receiver (such as headphones or speakers). If one doesn’t support aptX, the audio connection will be done via a more basic codec (often SBC), and quality will then be limited by this weak connection.
What’s more, to take full advantage of aptX, you also need to use good quality audio files. A simple, low-bitrate MP3 won’t do the trick. On the other hand, with FLAC or WAV, the difference can be noticeable on good equipment. Streaming platforms such as Deezer, Amazon Music and Qobuz offer hi-fi quality, so you can make the most of aptX.
aptX: a free, open-source codec
Previously subject to paid licenses, Qualcomm made the aptX and aptX HD codecs open source in 2023 for free integration into Android. This change allows smartphone and audio device manufacturers to offer these technologies without having to pay certification fees or royalties. By making these codecs accessible, Qualcomm hopes to broaden their adoption, particularly in entry-level and mid-range products, while supporting sales of its own audio chips.
This decision comes against a backdrop of strong competition, with alternatives such as Sony’s LDAC or Huawei’s LHDC already occupying the field of high-quality Bluetooth. Although more advanced versions such as aptX Adaptive or aptX Lossless remain subject to licensing, the opening up of basic versions could improve the overall sound quality of affordable wireless audio equipment. Qualcomm is therefore betting on a volume strategy rather than licensing to maintain its influence in the Bluetooth audio market.
aptX is a family of Bluetooth codecs designed to improve sound quality and reduce latency. While it doesn’t totally eliminate compression losses, it does enable users to listen to wireless music in much better conditions than with conventional solutions. For discerning music lovers who want to combine wireless comfort and sound fidelity, aptX is worth considering.
