What determines the audio quality of Bluetooth headphones

What is the difference between Bluetooth A2DP and aptX?

Bluetooth headphones are on everyone's lips for most of a decade as a niche restricted to tech enthusiasts. Now you can find an incredible selection of bluetooth headphones on the shelves of electronics stores and even more online. As with almost all product categories, however, not all wireless headphones are created equal.

We're going to talk about three Bluetooth technologies that determine exactly how good your Bluetooth headset sounds and what to look for in a new pair. A2DP is the basic Bluetooth stereo streaming protocol, aptX is an advanced codec designed specifically for Bluetooth, and Apple's W1 chip system is proprietary and only works with Apple hardware.

A2DP: The default setting

A2DP stands for Advanced Audio Distribution Profile, which means - well, it doesn't mean much in relation to something that already has audio streams in it. As one of the oldest parts of the combined Bluetooth specification, A2DP is more or less the default setting for streaming audio over Bluetooth. Every Bluetooth audio product you buy - headphones, speakers, cell phones, laptops - supports at least A2DP, regardless of whether it also works with aptX or not.

The A2DP standard operates in stereo and supports most of the standard audio compression codecs. The recommended subband codec (SBC) supports up to 345 kilobits per second at 48 kilohertz. This is about a third of the quality of standard CD audio - roughly the equivalent of a high quality MP3 recording. Due to the high "lossy" compression in the SBC codec, the audio quality is considerably worse in a range of 256 kbit / s.

The system also supports other popular methods of encoding and compressing audio such as MP3. If the audio source is already compressed in a format such as MP3, AAC, or ATRAC, it does not need to be re-encoded in SBC to be sent from the source device. With the maximum audio bandwidth of A2DP of 728 kbit / s, it is at least possible to achieve what we call "high quality audio" with the basic standard. (CD quality audio, uncompressed, is approximately 1400 kbps.)

Unfortunately, very few hardware manufacturers seem to actually use this feature, and most A2DP-only devices re-encode audio to SBC and decode it on the receiving end. This complicates the whole process and results in poor audio quality.

aptX: The upgrade

AptX is also a compression standard like SBC or MP3. However, it's better overall and designed for the limited bandwidth and low power consumption of Bluetooth devices. CSR, the developer of aptX, states that it uses a proprietary compression method that preserves the full frequency range of the audio while simultaneously "compressing" it onto A2DP's limited data pipe.

In layman's terms, think of the A2DP profile as a McDonald's hamburger with two quarter pounds and aptX as the “special sauce” that makes this burger a Big Mac.

The company claims that this advanced compression, the result is CD-like sound quality. A complete aptX system sounds a bit embellished, but significantly better than most pure A2DP systems. The codec can also encode and decode faster, resulting in less gap between the screen and speakers when watching a video with Bluetooth audio enabled. AptX HD is an even higher quality standard with 24-bit / 48-kHz audio and streaming at a slightly higher bit rate.

Unfortunately, aptX requires the codecis supported by both the radio and the receiver. If your headphones or speakers don't support aptX, they will only use A2DP by default, resulting in lower Bluetooth sound quality that you may already be frustrated with.

Apple's AirPods and W1 chip: the other

What about the iPhone? Does it support aptX and is it used by these fancy AirPod wireless headphones? No While the AirPods use Bluetooth (not AirPlay, which is more of a Chromecast Wi-Fi audio protocol), they use a proprietary W1 Bluetooth chip that is only available from Apple devices running iOS 10.2 or Sierra 10.12 ( or newer) is fully supported. This bespoke connection allows for greater fidelity than standard A2DP (and a near-instant automatic connection), but is not compatible with aptX. If you connect your iPhone to an aptX-enabled headset or aptX-enabled speaker, the low-fidelity A2DP will still be used.

There are other headphones compatible with the proprietary W1 enhanced Bluetooth standard: Beats. (Apple bought the Beats brand back in 2014.) In addition, both the AirPods and the W1-enabled Bluetooth Beats headphones can be connected to normal audio sources that are not intended for the iPhone. However, new Beats products don't use aptX either, and since Apple doesn't seem interested in licensing W1 technology for aptX, the AirPods or Beats headphones are basically the only choices for high quality wireless audio on iOS.

Note: You can use AirPods or Beats with third-party devices or with Apple devices running older versions of iOS or Sierra. These devices simply cannot take full advantage of the W1 chip. They establish a perfect connection via normal Bluetooth and use A2DP by default.

How do you know you are getting aptX?

First, check your current device, most likely your cellphone. Most of the newer phones sold in the past few years have this feature, especially those with Qualcomm Snapdragon processors. High-end phones from Samsung, LG, HTC, Sony, Huawei, and OnePlus all support aptX Bluetooth streaming. Apple's iPhone is an exception.

Next, make sure your receiving hardware is your speakers, car radio, or headphones - supports aptX too. This is less common and you'll want to check the datasheet to see if aptX is listed. It used to be limited to the most expensive models, but prices have come down recently. Typically, you can find aptX support for a wide variety of designs. Everything from a $ 400 pair of Sennheiser noise-canceling round-the-ear sockets to a $ 26 set of inexpensive Aukey earbuds can handle the aptX codec. Pay special attention to the support of aptX HD for even better audio quality.

Unfortunately, it can be difficult to determine whether the current audio you're playing on your device supports aptX streaming. Phone manufacturers in particular seem to be poorly informing the user about the codec or bit rate that is actually being used for audio transmission. Once you've made sure that both your player device and audio device are compatible, you usually need to play it by ear.

Image source: Sony, Amazon, Samsung, Apple