Bluetooth headphones: the eternal struggle with incomprehensible phone calls

My first office job didn’t just introduce me to the joys of everyday working life – it’s also where I discovered the benefits of hands-free calls. Instead of using a physical handset, I just had a headset that was connected wirelessly to my PC. When I wasn’t at work, holding my mobile phone to my head or getting tangled up in cables while making calls soon started to feel pretty old-fashioned.

Then, in late 2016, Apple launched the AirPods, opening the Pandora’s box of Bluetooth along with it. It wasn’t long before the market was flooded with wireless earbuds, a trend that’s showing no sign of stopping.

The result? Hours of hands-free calls.

Pretty great, right? Well, not quite…

When the call becomes a battle

You probably know the struggle. When you’re talking on the phone to someone wearing Bluetooth headphones, the other end of the line usually sounds rubbish. With your own Bluetooth headphones, it’s the same story. As soon as you start using them to make calls, the audio quality drops. So, how exactly does this happen? After all, you can listen to music in hi-res via Bluetooth these days.

It’s safe to say wireless headphones are perfectly capable of transmitting audio signals in high resolution. So, is the large distance between your mouth and the microphones in the earbuds to blame for muffled voice audio? It’s an obvious question – and one that doesn’t fall entirely short of the mark. Manufacturers tout new Bluetooth headphones with «improved microphones» and «smart voice recognition algorithms» year after year. And yet, the sound quality on calls remains poor. But why?

The Wild West of Bluetooth profiles

Not all Bluetooth is made equal. The wireless transmission standard comes in numerous versions, or profiles. This is the very thing that brings us to the heart of the quality question. A2DP (Advanced Audio Distribution Profile) is used as standard when listening to music or watching movies.

It’s the profile responsible for transmitting audio signals from a transmitter to a receiver. So, when you’re listening to music on Spotify or Apple Music, your phone is the transmitter and your headphones are the receiver. This involves various well-known Bluetooth codecs such as SBC, AAC, AptX or Sony’s LDAC, which can transmit content at up to 32 bits and 96 kHz. In short, A2DP delivers extremely high sound quality by Bluetooth standards.

But here’s the catch. With this profile, signals can only be transmitted in one direction. However, if a set of Bluetooth headphones and its built-in microphones need to be used both as a receiver and transmitter, you have a problem.

It’s all in the direction

When this happens, the devices you’re using automatically switch to HSP or Headset Profile. Technology-wise, this profile is very outdated, and can only transmit at 8 kHz. It certainly doesn’t offer «modern» features such as stereo sound. Even so, the profile has its raison d’être.

Unlike A2DP, HSP also allows devices to control each other. In other words, with this profile, you can use your headphones to answer or end a call on your phone. HSPs also used to display the battery status of your Bluetooth headphones and control the volume.

All of this applies to calls placed using an internet connection as well as video calls. You might’ve noticed that your Bluetooth headphones continue to sound bad after a Zoom call has ended, with the problem only disappearing once you’ve reconnected your headphones. Sometimes, your headphones can also get «stuck» in HSP, and don’t switch back to A2DP automatically.

Are there any improvements on the horizon?

Naturally, I’ve only gone into the theory underpinning the sound quality question. In practice, things are a little different. Not every mobile phone or set of headphones supports every profile and codec, which can lead to connection problems. Not to mention the Bluetooth network, which tends to be under full load. I might write about the latter in more depth in the future.

To sum all this up, not all Bluetooth is the same. There are various profiles each suited to different purposes. A2DP enables transmission of high-resolution audio signals in one direction, while HSP allows two or more devices to interact with each other.

Basically, it’s a question of choice: would you rather hear the audio at full quality or use the microphones on your Bluetooth headphones? Unfortunately, it doesn’t look like we’ll be able to reconcile the two in the foreseeable future. Bluetooth as a transmission standard is constantly being developed and improved. As things stand today, however, the technology is fundamentally flawed and our phone calls will continue to sound muffled. Unless you do things the old-fashioned way and hold your phone to your ear, that is.

Header image: Dayan Pfammatter