In pushing wireless earphones to the world , Apple played a role. With the removal of the headphone jack from the iPhone 7, the company made it clear that the future of audio is wireless. However, the company had already noticed its vision before the iPhone 7 with the original Apple Watch. Years later, the company continues to remove the jack in more devices like the iPad Pro.
Today, we’re working on wireless audio.
Specifically, the different Bluetooth audio codecs and why they will play an important role in the future of audio. Earlier this year, we broke down Bluetooth 5.0 and its role in driving the wireless revolution. Learn more about it here. compression First, let’s talk about audio compression. Compression is an algorithm in which some audio is removed (compressed) to reduce file size. Modern compression algorithms are usually very good at this and remove frequencies that are inaudible to most people.
Next comes the muddy waters of lossless vs. lossy, two completely different compression methods despite sounding the same. Lossy is what most music streaming services use. This compressed form has bit rates between 256Kbps and 320Kbps in various formats (eg OGG, MP3, M4A). As far as lossy compression goes, it doesn’t matter as long as the format and bitrate fall between 256 or 320. For example, OGG 320Kbps is used on Spotify, and 256Kbps M4A is used by Apple Music and iTunes Store.
Lossless is where things get controversial. Lossless is defined as an audio file that usually has a bit rate higher than 500Kbps and comes in various formats such as FLAC, WAV or ALAC. By definition, lossless audio means that nothing is lost and all artifacts and details remain in the original recording. The reason for the controversy is that some audiophiles believe they can hear the difference in audio quality, contradicting the popular belief that lossy compression is fine for most people. Generally, you won’t find a lossless file unless you delete from a CD, look specifically for it, or stream through TIDAL.
This is important because Bluetooth audio compression varies by codec. There is a common misconception that Bluetooth audio will never be as good as wired due to its compression method, but that’s not the case. Some codecs allow lossy, while others allow completely lossless audio streaming.
So let’s talk about codecs.
On the baseline, each set of Bluetooth headphones (or speakers) uses a low-complexity subband codec, better known as SBC. While it generally has a bad reputation among the worst compression methods, SBC doesn’t actually have any bitrate limits. However, manufacturers usually set the maximum bitrate to 345 Kbps. SBC is free for manufacturers to use and is the first audio codec to be certified for Bluetooth. Today every bluetooth audio device supports SBC as a backup, some devices only support SBC.
Next up is Advanced Audio Coding, better known as AAC. This codec is commonly found in Apple devices, and Android has recently supported the codec in later versions of the operating system.
AAC has basically become the standard for Bluetooth audio. This is both good and bad. For the bad: it’s not an open standard and manufacturers have to pay for a license. On the other hand, having AAC as a Bluetooth codec means that audio encoded with AAC, whether MP3, M4A or ALAC, does not need to be compressed when sending the audio from the device to the headphones. This means wireless audio is not “compressed” over the air. In theory, anything encoded with AAC will sound the same whether it’s over bluetooth or over the wire.
In theory, that’s why Apple only supports SBC and AAC on its devices. All content purchased or streamed via iTunes or Apple Music is encoded via AAC. The only exception is Mac, which supports aptX.
Speaking of aptX, this is the next logical Bluetooth codec supported by the device, and it comes in a few different flavors. First, aptX was developed by Qualcomm. This means that most, if not all, Android phones support aptX, since most Android phones have Qualcomm processors built into them.
As mentioned, no Apple device actually supports aptX other than Macs. This means that while your headphones support aptX, most Apple devices will default to either SBC or AAC, as they only support those two codecs. The basic aptX codec is a lossy format, similar to SBC, that requires re-encoding audio files as they are transmitted over the air to your headphones or speakers.
This is where things get more interesting. Next to aptX, you have aptX-HD, which is also developed by Qualcomm, but uses a slightly higher bitrate, around 576 kbps. aptX-HD provides “high definition” audio that can be sampled up to 48 KHz at resolutions up to 24 bits. At this point, you have what is called a “hybrid” codec, because it’s not technically completely lossless, but “closer to lossless”. Some audiophiles swear by aptX-HD and don’t buy anything that doesn’t support this codec.