Ever since Apple decided to ditch the headphone jack, wireless audio saw a rise in popularity. The Bluetooth headphones transmit sound using Bluetooth audio codecs. In this article, you’ll learn what that means and whether it’s important for you. Bluetooth is the name of the wireless connection, whereas Bluetooth codecs are responsible for the sound quality that hits your eardrums. In this article, we’ll take a look at: How Bluetooth worksHow it transmits dataWhat are Bluetooth audio codecsWhich one you should look for Table of Contents Terminology When looking at the specifications of the audio codecs, you see a lot of numbers. To avoid confusion, let’s break down specific terms: Sample Rate Analog audio looks like a series of waves. To digitalize those “waves,” you need to take samples of how far up or down are those waves. When you take enough samples, you can later recreate the same waves to the original. In practice, the minimal sample rate used is 44,100Hz, which means 44,100 samples in a second. You can also find recordings taken with 48 to 382kHz samples, but those are larger files. Bit Depth In audio, there is something called dynamic range. It is used to determine the distance between the quietest and loudest sounds in the recording. How good the dynamic range, aka how much data is stored in the file, is marked as the bit. Most audio codecs have a bit depth of 16-bit, which is the same as the quality of the CD. However, some DVDs and Blu-Rays, as well as studio recordings, can go up to 24-bit or even 32-bit. Bitrate Bitrate tells you how much data is being transferred from point A to point B. Most of the time, you can see the bitrate value of 320kbps (kilobits per second), which is the highest value of MP3. The lower you go, the worse sound quality and dynamic range you can expect. You get the bitrate speed when you multiply the Sample Rate, Bit Depth, and the number of channels. Psychoacoustics A study of how humans perceive sound. Studies have shown that there are certain sounds inside recordings that people are not able to hear. For example, if you have one peak in between 2 higher peaks, the lower one isn’t audible, so it’s deleted to save space. That is how many lossy audio codecs came to life, including MP3. Compression Speaking of a lossy codec, we know 3 different compression methods that are mainly there to save space on our devices. Uncompressed: all data is preserved, is associated with codecs such as WAV and AIFF Compressed Lossless: all information is preserved, smaller file sizes, associated with codecs such as FLAC and ALAC Compressed Lossy: redundant data is lost (based on psychoacoustics), files can be really small, associated with a codec such as MP3, AAC, WMA Encoder/Decoder It relates to a software solution that needs to pack (encode) the data to be later transferred on another device, where the same data is unpacked (decoded). Every codec has its encoder and decoder. For example, only an aptX decoder knows how to unpack the data packet from an aptX encoder. How Does Bluetooth Work When Transmitting Audio? Because all the data transfers happen wirelessly, the performance highly depends on the situation. When two Bluetooth enabled devices pair, the quality of transmission is chosen by a receiving device. When the connection is perfect, audio is transmitted using the best Bluetooth codec available. But if there are obstacles in the area that would hurt the connection (other people’s Bluetooth devices or getting too far away from the source), the Bluetooth chip decides to downgrade to codec quality to preserve the connection. Thankfully newer generations of Bluetooth are quite robust and can work even busier environments. However, if there is a bus full of wireless headphone users or multiple Bluetooth devices connected to one device, interferences are inevitable. Bluetooth Audio Codecs At the beginning of this article, we said that Bluetooth is just a connection and that the codecs determine how good the transmitted data will be. The Bluetooth codec is in charge of how your audio files will be “chopped” and then put back together inside the receiving device. The more data it needs to be transferred, the more energy is used. With the devices as small as earbuds, these Bluetooth codecs strive for the most optimal compression, trying to preserve high fidelity, while transmitting with low bitrates. Of course, low-bitrates don’t necessarily mean bad sound quality, since it also matters how smart the compression is. For example, AAC has a lower bitrate than SBC but is still considered to transmit higher quality audio. Quick Comparison of Bluetooth Codecs Bluetooth Audio CodecSupport for HD AudioMax. BitrateMax. Bit DepthMax. Sample RateSBCNo345kbps16-bit48kHzAACNo250kbps16-bit48kHzaptXNo354kbps16-bit48kHzaptX HDYes576kbps24-bit48kHzaptX LLNon/an/an/aaptX AdaptiveYes420kbps24-bit48kHzSony LDACYes990kbps24-bit96kHzLHDCYes900kbps24-bit96kHzLLACYes600kbps24-bit48kHzSSCYes512kbps24-bit96kHzLE-Audio-LC3Yes345kbpsn/an/a SBC (Low-Complexity Sub-Band Codec) Despite its bad reputation, SBC can be quite flexible when it comes to audio quality. It can transmit bitrates up to 345kbps, which is higher than MP3. Although the speed can drop to 128kbps if the connection gets worse. It also supports sample rates of 48kHz. In most cases, the difference between higher quality codecs is minimal. In noisy environments, even unnoticeable. It does suffer from a significant lag when watching videos. However, SBC is not the only one with this problem. Some manufacturers also put additional chips inside their headphones to minimize delays, such as in Jaybird Vista (review). Jaybird put JBS1 chip inside the Vista model, which ensures better connectivity and reduces video lag. This codec is integrated into A2DP (Advanced Audio Distribution Profile), which means that every Bluetooth device has it. It’s also the only one free to use (for other codecs manufacturers need to pay a fee). Therefore, if the connection gets terrible, or your device does not support the best codec from your headphone, it will then choose SBC. AAC (Advanced Audio Coding) It uses more aggressive compression but preserves more data than an MP3 file format. When used in Bluetooth to transfer data, the processing power required to decode and encode consumes more energy. The spec sheet shows that AAC is quite similar to SBC, but because it’s more advanced, the end quality is noticeably better. However, it does need to be implemented in the right manner. Apple is doing a tremendous job at that. They have the best encode software, and it shows. Their wireless headphones work like a charm (Apple AirPods Pro). AAC also has different implementations like SLS (Scalable To Lossless), which can transfer lossless audio wirelessly, and even AAC-LD (Low Delay), that is used to reduce latency. Whereas SLS is standardized for Bluetooth, AAC-LD is not. Unfortunately, there are no devices that support these two codecs. aptX AptX outperforms SBC when it comes to both the audio quality and latency. The latter is essential while watching videos. It was developed to bring the “CD-like” experience to your wireless headphones and speakers, although that is a bit exaggerated. It’s still quite common in Bluetooth equipment and has a good implementation on Android. Every phone with Android has support for the aptX. Audio codecs that start their name with “aptX” are owned by Qualcomm, a company mostly known by their mobile processors. The codec was patented back in 1988, long before Bluetooth, and it was used for professional audio equipment. aptX HD (high-quality Bluetooth audio) It has a better encoding profile, ensuring higher bitrates (576kbps) compared to regular aptX. It can transfer up to 48kHz sample rates and 24-bit depth. The result is an overall cleaner sound experience, with better dynamic range. It’s still a lossy codec, although the loss of data is kept to a minimum. However, not many devices support this codec. You can find it on phones from LG, Huawei, Sony, HTC, OnePlus and Google, and inside some headphones from Audio-Technica, Bowers & Wilkins, Beyerdynamic, and Nura. aptX LL (Low Latency) This codec is by far the best solution if you’re irritated by a delay in videos or games. Because it offers low latency of just 32ms, the lag is practically invisible to the naked eye (and ear). If you tend to only listen to music, this codec isn’t that important to you. Also, aptX LL is fairly new, so not many devices have support, and so far it only works on Windows 10. aptX Adaptive Considered the audio codec of the future, it combines all of the aptX codecs mentioned above. That is why it’s able to transmit HD quality Bluetooth audio with high dynamic range, while still keeping the latency very low. The compression algorithm has also improved, having now the same level of sound quality at 420kbps, compared to 576kbps of aptX HD. aptX Adaptive is backward compatible, but you’ll have to buy a pair of headphones that support the new codec if you want to get the most out of it. Sony LDAC Yet another Bluetooth solution owned by a big company. LDAC is by far the most CD-like of the bunch, offering an impressive bitrate speeds up to 990kbps. It does so by maintaining the sample rate of 96kHz and a bit depth of 24-bit. Different modes determine the bitrate speeds: Connection priority (330kbps), Normal (660kbps), and Quality priority (990kbps). LDAC is available on every phone that uses Android 8 or above. However, there aren’t many headphones that support this codec. One of the most popular ones is the Sony WH-1000XM3. LHDC and LLAC (Low Latency and High Definition Audio Codec) These two codecs are owned by HWA Union (Hi-Res Wireless Audio) and Savitech. With them, they want to rival the likes of aptX HD and LDAC. LHDC offers some impressive specs, giving you a bitrate speed of up to 900kbps. With a maximum of 600kbps, the LLAC is slightly worse, but still pretty good, insuring the latency of just 30ms. Sadly, the only phones that support these two codecs are from Huawei. Samsung Scalable Codec Samsung is also a new player in Bluetooth audio codecs, with their solution being very similar to AptX Adaptive. It has a variable bitrate from 88 to 512kbps. Speed is decided by analyzing environmental interferences. Since the codec is relatively new, only Galaxy S20 line-up and Galaxy Buds+ true wireless earbuds support it. Samsung Galaxy Buds+ are the first true wireless earbuds to have Samsung Scalable Codec. Bluetooth LE Audio LC3 At the beginning of 2020, we were greeted with the arrival of Bluetooth Low Energy Audio codec. With the LE Audio also comes LC3 (Low Complexity Communications Codec), which is making sure the audio is transmitted in high quality and with low energy consumption. More than insane bitrate speeds, the new codec brings an overall more fluid experience. For example, when going too far from the Bluetooth transmitter, the degradation in sound will be much smoother. LC3 also supports multi-stream broadcast, meaning you can transmit one stream to one wireless earbud and a different stream to another. Of course, at the cost of bitrate speed. LE Audio has also found its way into hearing aids, giving you an option to stream audio directly to your earpiece. Which Bluetooth Audio Codec is Better, and Does it Make a Difference? That is a heated debate among the audio community since everyone thinks differently. On paper, all of these codecs have specific benefits over the others. But in reality, there is a barely noticeable difference between them. The low tier SBC, AAC, and aptX are quite similar in regular use. aptX has an advantage when it comes to video lag, but AAC works excellent on Apple. But pair SBC with a chip that ensures stable connection and no lag audio, and you’ll have a hard time distinguishing one from another. That being said, you’re getting the best experience from high-quality Bluetooth codecs such as aptX Adaptive, LDAC, and LC3. But more than perceived high sound quality, you’re getting better responsiveness, features, and efficiency. It’s much more important how a Bluetooth headphone or speaker can output the best sound quality. No codec can change a lousy tuning, driver, or enclosure design. There is also this trick that manufacturers like to implement, which gives you a sense of a specific codec sounding better or at least different than the other. DSP (Digital Signal Processor) handles all the incoming audio signals in your headphones, applying EQ to the overall sound. Sometimes DSP can have different settings for a specific audio codec, resulting in a changed sound. To sum up: If you’re an Android user, consider using something with the support for aptX. That way, you’re getting good audio quality and low-latency experience when watching videos on YouTube. Suppose your OS of choice is iOS, then AAC is the best pick. Apple is using this codec for a long time, and they implemented it well to work with their system. What Else Can Affect the Bluetooth Audio Quality? As we know by now, the quality of the connection directly affects the bitrate speeds. Bluetooth might be losing its strength because of: Being too far away from the transmitter – Bluetooth 5.0 works flawlessly up to 10 meters (33ft), but once you go past that, quality starts to degrade slowly. Try maintaining the distance in a radius of few meters, just to make sure. Obstacle(s) between two devices – Bluetooth is operating on the 2.4GHz, which can have no problem being transmitted inside the smaller room. However, this kind of frequency struggles to penetrate through solid objects. It can pass one brick wall quite easily, but going past the second one is almost impossible. Electromagnetic interference – Since Bluetooth is essentially electromagnetic radiation, other devices that create the same kind of frequency can interfere with it. Those can be other phones, WiFi, even microwaves. Sometimes even a glass of water can obstruct the connection, with water acting as a frequency absorbent.