Bluetooth Codecs Explained: AAC, AptX, LDAC and More

Being able to wirelessly connect headphones and speakers to your phone or computer is a magic many of us take for granted. It wasn't that long ago that the idea seemed impossibly futuristic. These days, you can get true wireless Bluetooth earbuds for less than a meal at McDonald's and BT speakers that can blow you out of the room.

But there's more to Bluetooth than a simple wireless connection. Bluetooth is the conversation, but the codec is the language being spoken. In the early days, high-fidelity audio seemed just as impossible as wireless had only a few years before. Today, a range of codecs promises audio quality the MP3 era could only have imagined.

Not every headphone or earbud can understand every codec that's out there. Not every source, like your phone, laptop or portable media player, can transmit every codec, either. So here's what they all mean, what you might want to consider and -- most of all -- whether any of it really matters.

What's a codec?

This diagram, via Sony, illustrates the challenge of sending audio data wirelessly to headphones. With hi-res -- and even standard CD-quality -- audio, the data must be compressed to fit through Bluetooth's limited "pipe." Streaming audio, including compressed formats like MP3 and AAC, is re-encoded again for wireless transmission. And for a more stable Bluetooth connection, lower bit rates are generally more reliable.

Sony

"Codec" is a portmanteau of coder/decoder. A source encodes some data, and on the playback side (your headphones, say), a decoder converts that data into a form it can use. Nearly everything we use in the modern digital world uses a codec of some kind. Talking to your friends on the phone, watching Netflix, listening to Spotify -- there's some kind of codec at work. 

There are countless types of codecs across different technologies, and Bluetooth has several possible codec options of its own. Think of Bluetooth as a phone call between two people: They might speak French, English or even Klingon. Bluetooth is just the connection -- the language they use is the codec. There's more to it than this, but that's the general idea.

Conveniently, deciding the codec "language" is usually done automatically once you connect the devices. Your phone and earbuds, for example, will do a little handshake -- an agreement on which language they'll speak. In some cases, you can force them to speak a different language, but I'll talk about that in a moment.

While the end result -- music in your ears -- is the same, the various codecs differ in important ways. One important aspect we'll be discussing is bit rates, essentially how much data is used per second to transmit the audio. Think of it as the size of the pipe, so to speak, between your earbuds and phone. A bigger pipe is often better, but not always. I'll dive into that, too. And keep in mind that these codecs are separate from the ones used to encode the music originally. Even though some share the same names, these codecs are specifically for the wireless transmission of the audio.

The basics: SBC and LC3

Bluetooth SIG

The creators of Bluetooth decided early on that there needed to be some sort of "lingua franca" so all devices could communicate at a basic level. Without this functionality, Bluetooth would never have become as popular -- and nearly ubiquitous -- as it is now.

The common language for Bluetooth is called SBC, or "Low Complexity Subband Coding." It was designed to provide reasonable sound quality but, more importantly, to require minimal processing power so it wouldn't drain battery life. All Bluetooth devices have to support SBC. The sound quality can theoretically be quite good, but it can vary significantly depending on how it's implemented by a manufacturer. Because it's a fairly simple codec -- at least compared to some others -- lower bit rates can negatively affect the sound. Which is to say, SBC can sound pretty bad, but it's not accurate to say "SBC sounds bad" in general. It's more accurate to say "SBC sounds bad on these specific headphones."

Bluetooth SIG's replacement for SBC is called LC3, and it claims to offers better sound quality at lower bit rates. Expect to see more LC3-compatible devices going forward.

Bluetooth SIG

Starting with Bluetooth 5.2, the newer Low Complexity Communications Codec, or LC3, has become an option for manufacturers as part of LE Audio. The promise of LC3 is higher audio quality at the same, or potentially lower, bit rates. 

Most mid- and higher-end Bluetooth earbuds and headphones include additional codecs that promise the same benefits, often with a more audiophile reputation. Bluetooth SIG, the organization behind Bluetooth, even has an interesting comparison test on its website for LC3, where you can compare SBC and LC3 to the uncompressed original tracks at various bit rates.

Because it's fairly new, LC3 is less common than most of the other codecs we'll discuss. Remember, both the source (your phone, for example) and the headphones need to support a codec for it to work, so you might also need a new phone to get LC3 to work with your next pair of LC3-compatible headphones.

* Generally, this is the highest potential bit rate, though some implementations can be lower on specific devices. Bit rate alone is not enough to determine audio quality. For instance, AAC and SBC have psychoacoustic modeling, like MP3, so by discarding audio data, you (theoretically) can't hear they're capable of better apparent sound than their bit rate alone would suggest.

The next step up: AptX and AAC

Apple devices use AAC.

David Carnoy/CNET

Apple's codec of choice is AAC, or Advanced Audio Coding. Confusingly, this is also the name for Apple's iTunes alternative to MP3 for music files. In terms of Bluetooth, it's a more complex codec than SBC, so it potentially sounds better at similar or even lower bit rates. This is why judging any codec based solely on its bit rate is folly. Historically speaking, AAC has sounded better on iOS devices than on Android due to how both handle the encoding. These days, since Android phones typically support some form of AptX in addition to SBC, there's rarely a reason to force AAC on an Android device. The good news for Apple users, since they have no other option, is that AAC is quite good, especially considering its low bit rate.

Qualcomm

On the Android side is the AptX coat of many colors. AptX is owned and developed by Qualcomm. In some ways, AptX is to Android phones what AAC is to Apple, but the specifics get more complex. 

There are multiple flavors of AptX, and both the source and the device need to support the same variant, yet it's often difficult or impossible to know which one you're actually using. While SBC can sound worse depending on how a manufacturer configures it, Qualcomm sets a minimum performance level for AptX that's higher than SBC's lowest settings. In other words, SBC can sound worse than AptX, but it can also sound very similar.

AptX: The base version of AptX is typically only seen on older gear now. If no other version is shared between devices, they'll default to basic AptX (instead of SBC).

AptX HD: Originally developed as a step up in quality over regular AptX, it promises higher bit rates (up to 576 kbps) and higher bit depth (24 versus the more common 16). Most of its features were largely rolled into AptX Adaptive.

AptX Low Latency: The processing required to transmit audio over Bluetooth takes a little time. When you're listening to music, this isn't noticeable. If you're gaming and there's lag between something happening on screen and when you hear it, this latency can be annoying. AptX LL promises latency as low as 30 to 40 milliseconds, compared to the several hundred milliseconds possible with other formats. Not particularly common, some of LL's features were rolled into AptX Adaptive.

AptX Adaptive: Qualcomm's latest version of AptX rolls a lot of the features of its predecessors into one single variant. It has the potential of low latency (though only down to 80 milliseconds) and the potential of higher bit rates, up to 420 kbps in most situations. While a catch-all for different AptX features, its main claim to fame is being able to smoothly vary the bit rate to maintain audio when the signal would otherwise cut out. Unfortunately, you can't really tell what you're getting in terms of quality. It adapts, but what it adapts to is obscured. Also, the specific implementation varies. Just because a device has AptX Adaptive doesn't mean it has all the possible features. This isn't very clear to the consumer.

Qualcomm

Additionally, Qualcomm uses "Snapdragon Sound" in its marketing, which indicates that the product supports higher-quality forms of AptX, including -- but not requiring or limited to -- AptX Lossless.

Higher fidelity (in theory): LDAC, AptX Lossless  

There are two semi-common codecs that promise even higher quality audio. These definitely have higher bit rates, but as we've discussed, bit rate alone doesn't determine sound quality. The "holy grail" of Bluetooth audio is lossless transmission -- where the data on your phone reaches your ears with no reduction in quality. But because this requires extremely high bit rates, it isn't very robust. You might not get a stable connection to your headphones even if your phone is sitting on your desk. There's also the question of how much better these codecs actually are compared to the "lesser" but far more efficient options, but we'll get to that later.

Sony

Sony's LDAC is its own take on a Bluetooth codec. It's typically found only in Sony headphones, but on the source side it's available on a fairly wide range of Android phones. Like AptX Adaptive, it has a variable bit rate (330, 660 or 990 kbps), so it can work in less ideal environments. However, also like AptX Adaptive, it might default to one of its lower settings. If so, it's not any better than other options. If you're going to use LDAC, you'll need to go into your phone's developer settings to force it to go to its highest quality option. How high that is also varies. In theory, you should be able to get CD-quality audio, or just about, losslessly from source to headphones at the highest bit rate.

AptX Lossless has the potential of up to 1,200 kbps, pushing the absolute maximum bandwidth possible with audio over Bluetooth. Qualcomm says this allows for the lossless transmission of CD-quality audio. However, like LDAC, if the data rate isn't sustainable because of environmental or distance factors, it'll drop down to a lower bit rate -- in this case, to a version of AptX Adaptive instead.

There are other, even less common codecs you might encounter in the occasional product, now or in the future -- including MQair from the company behind MQA, Samsung Seamless Codec and LHDC or L2HC. Unless your phone or audio player and your headphones or speaker support one of these, they're not worth worrying about until they become more widely available. Manufacturers often create their own codecs to avoid licensing an existing one. Are these better? Maybe. Are they saving the company money? Probably. Are they different enough to worry about? Well...

Does it matter?

David Carnoy/CNET

So after all that, how much does the codec really matter? Hot take incoming: Not a ton. Don't get me wrong, with a decent pair of headphones, a quiet listening environment and a high-quality stream or download, you'll likely be able to hear the difference between SBC at its worst and one of the better codecs at their best. But that difference is going to be pretty subtle unless something is very wrong. Plus, it's basically impossible to say that even if you do hear a difference, what you're hearing is the codec itself. There's enough variation in how all of these are implemented that you could easily be hearing something else in the chain.

What will have a far greater impact on your sound quality than the codec are, in order: better headphones, a better fit/seal, listening in a quiet place and even improving the quality of the music stream itself (Qobuz, Tidal, and Apple Music all have higher resolution than Spotify, but at least Spotify finally has lossless). These aspects will all improve your sound far more than changing the codec between your source and headphones.

If you have changed all of the above and want to squeeze out every bit of sound quality possible, it may be worth spending a few minutes checking your phone's settings to see which codecs it supports. (Well, on Android anyway -- iPhones are just AAC.) Sometimes the phone or audio player defaults to a safe but poor-sounding option. And, frustratingly, just because a codec appears in the hardware specs doesn't mean it will actually work. Even if it does, and works great at home, it might be unusable in environments with heavy wireless interference or when you're trying to listen in one room while your phone is charging in another.

Which is all to say: Changing the codec on your phone or tablet isn't going to magically make $150 earbuds sound like $500 earbuds. That's just not possible unless something was set wrong to begin with. It might, however, make what you have sound a little better, or give you a more reliable connection when you're out and about.

Lastly, if you're trying to decide between two headphones and one is lauded for its sound quality but "only" has AAC/AptX versus another that reportedly sounds OK but has LDAC or AptX Lossless, choose the one that sounds better over having additional codecs every time.

In addition to covering audio and display tech, Geoff does photo tours of cool museums and locations around the world, including nuclear submarines, aircraft carriers, medieval castles, epic 10,000-mile road trips and more.

Also, check out Budget Travel for Dummies and his bestselling sci-fi novel about city-size submarines. You can follow him on Instagram and YouTube.