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Bluetooth Codecs Explained

by Abheer Monga June 25, 2018 4 min read

Bluetooth Codecs Explained

Buying a ‘good’ pair of headphones can be really tricky if you don’t know certain important terms related to it. There are so many different options in headphones. In-ears, on ears, over ears, wired, wireless, etc. and each product has a platter of its own distinct features. While wired headphones have always been widely preferred, wireless headphones are breaking their way in. Authentic quality lossless music can now be streamed wirelessly thanks to the development of advanced audio codec algorithms. Confused? Let’s take it one complex term at a time.

How do you listen to songs from your device? By pressing the play button? Sure! But there is so much more to it than just pressing a button. Songs are produced and then stored in a digital format- the comprehensive language of all electronic devices. When you want to listen to these stored songs, your smart devices convert this digital information back to what is called the analogue format. The analogue format is what we listen to. This conversion of formats takes place due to the presence of a DAC (Digital to Analogue Converter) in our devices. Take a moment to absorb this in before we proceed.

Digital to Audio conversion sometimes affects the original quality of songs. Keeping the quality intact entirely depends on whether the song was compressed with minimum loss of elements. And, each and every Bluetooth headphone (yes, even that one you’ve been eyeing for sometime) has an inbuilt DAC.

To ensure compression of data without affecting the quality, developers have come up with advanced audio codec algorithms.

In terms of software, a codec determines how your audio files are transmitted from the source to your headphones (via Bluetooth). It encodes and decodes digital audio data into a specific format. Ideally, it transmits a high-fidelity signal at the minimum specified bit-rate. This results in the least amount of space and bandwidth required for storage and playback, respectively. A lower bitrate means better compression and worse sound quality, a high bitrate means better sound quality and worse compression. Let’s now have a look at the different types of codecs.

SBC- The default Bluetooth codec is Sub-Band Codec. The low-complexity Sub-Band Codec divides the signal into multiple frequency bands and encodes each one independently. It is the standard type that is mandatory over all A2DP-enabled devices, making it virtually universal. SBC is a lossy compression algorithm.This means that when it encodes music for playback, it literally drops pieces of music the algorithm deems low-priority, these are mostly sounds you can’t hear anyway because they’re masked by other sounds in the same frequency range at higher volume.

AAC- Advanced audio coding is the audio standard for lossy digital audio compression. It also happens to be the license-free standard for YouTube, Sony Playstation and is the preferred audio codec by Apple. AAC can transmit 250 kbps of audio data. If you’re using a pair of AAC-compatible headphones and streaming music via Apple Music, iTunes or your stored AAC files, you’re theoretically getting no loss in audio quality.

Qualcomm’s proprietary codecs: Qualcomm is the leading owner and developer of wireless codec algorithms that have enhanced the quality of music heard via Bluetooth. Qualcomm processors have been used in many popular brands of smartphones, including LG, Xiaomi and Microsoft (just look it up in the specifications and you’ll find it there).

aptX- The simpler aptX codec supports 48 kHz / 16 bit LCPM audio data (352 kbps). It supports a fine enough bit-rate to keep everything running smoothly and sounding phenomenal. Qualcomm says aptX was designed to bring “CD-like” quality audio over Bluetooth. So, if you’re listening to high-quality source files like FLAC at 16-bit/48kHz (a popular lossless compression algorithm) where both your phone and headphones are aptX compatible, you are listening in the best-case scenario for aptX and have reached the codec’s upper limitations. The technology must be incorporated in both the transmitter and receiver (i.e. your audio player as well as headphone) to derive the sonic benefits of aptX audio coding over the default sub-band coding (SBC) mandated by the Bluetooth standard. Products bearing the CSR aptX logo are certified for interoperability with each other. 

aptX HD- AptX HD is a Bluetooth audio codec that can transmit 24-bit/48kHz audio with a "gentle" compression at 576kpbs. Though both aptX and aptX HD are lossy formats, they’re leagues ahead of SBC. Higher quality audio can be sent using aptX HD without increasing the latency or pausing the data stream. 24-bit 48kHz files are true HD files where you hear very little background noise and can hear each individual element sounding clearly.

How is aptX HD better than aptX? Well, just imagine the difference between an mp4 and 4k HD video.

aptX LL- Your brain can’t tell the difference between a delay of 0 and 100ms. Therefore, audio transmission needs to happen at a rate of approximately 40ms to be heard in synchronisation with what you’re watching. Qualcomm aptX Low Latency supports 48kHz / 16bit LPCM. It ensures your wireless, Bluetooth enabled devices can deliver sound in sync with visual media. With aptX Low Latency you can enjoy the wireless freedom for applications such as gaming and watching videos.

LDAC- Like Qualcomm, Sony has its own proprietary Bluetooth codec, LDAC. Its variable bit-rate is the defining feature, which transfers up to 3x the data compared to SBC. It’s able to maintain a sample rate and bit depth at 96 kHz / 24 bit (maxed at 990 kbps). LDAC is compatible with all Sony devices and Android 8.0 Oreo and above versions.

 

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Abheer Monga
Abheer Monga



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