In short
Bluetooth headphones use one mode for listening, with a codec built for music, and another for calls that carries sound both ways at lower quality. Apple says quality and volume drop while an app uses the headset's microphone. Speak into another microphone to avoid the switch.
Bluetooth headphones talk to a Mac in two different ways. For listening, they use a mode built for music, with a codec that carries sound one way at good quality. For calls, when an app opens the headset's microphone, they switch to a mode that carries sound both ways at once, at lower quality. Apple's own support article puts it plainly: when an app uses the Bluetooth headphones' microphone, audio quality and volume are reduced until the microphone is no longer in use. That is why the call sounds flat in your ears and your voice sounds thin to everyone else.
This guide explains the two modes, what "codec" means here, what Apple recommends, and how to avoid the switch. Checked against Apple's support article If sound quality is reduced when using Bluetooth headphones with your Mac on 25 September 2026.
Two modes, two jobs
Bluetooth audio is defined by profiles, standard descriptions of how devices exchange a kind of data. Two matter for headsets:
| Listening mode | Call mode | |
|---|---|---|
| Bluetooth profile | A2DP (Advanced Audio Distribution Profile) | HFP (Hands-Free Profile) |
| Direction | One way: Mac to your ears | Both ways: your ears and the microphone |
| Quality | Good enough for music | Built for speech; narrower and flatter |
| When it is used | Music, video, a call with the headset microphone unused | Whenever an app opens the headset's microphone |
The Bluetooth link has limited room. In listening mode all of it goes to high-quality sound in one direction. In call mode it has to carry your voice back as well, so both directions get less. Newer headsets and newer versions of the standard have narrowed the gap, but the drop is still common and easy to hear.
Apple's support article describes it in the same terms: Bluetooth has a mode optimised for high-quality audio playback and another that supports two-way communication, and the switch happens when the microphone is used.
What a codec is
A codec is the method used to compress sound so it fits over the Bluetooth link, and to decompress it at the other end. Each mode uses its own codecs:
- In listening mode, the standard requires one basic codec, SBC, and allows others such as AAC. Which one is used depends on what the headphones support.
- In call mode, the codecs are designed for speech and carry a narrower range of sound. That narrower range is what makes voices sound like a phone line.
System Settings does not name the codec in use. You do not need to know it: the practical question is whether the headset's microphone is open, because that decides the mode.
What you notice
- The call sounds different the moment you join. Flatter, narrower, sometimes quieter.
- Music playing in the background drops in quality when a call app starts.
- Your voice sounds distant or muffled to the other people, or in a recording.
- Static or popping in some cases, which Apple mentions too.
- It goes back to normal when you leave the call, or sometimes only after you reselect the headphones.
Avoid the switch
The dependable fix is to not use the headset's microphone. Listen on the headset; speak into something else.
- Open System Settings › Sound.
- Under Output, choose the headset.
- Under Input, choose another microphone: the Mac's built-in microphone, a wired headset or a USB microphone.
- Make the same choice in the call app. Zoom, Teams and Meet each keep their own microphone setting, and it is often left on the headset.
The headset's microphone never opens, so it stays in listening mode, and you keep the main benefit of headphones: the other side's voices go into your ears, not your microphone. Recording a call with AirPods or a Bluetooth headset goes through this with AirPods specifically, and choosing the right microphone on a Mac shows every place the microphone choice lives.
If quality stays low after the call
Apple suggests three steps when sound stays reduced:
- Quit apps that use the headset's microphone, such as call and chat apps.
- Close System Settings if it is showing the Sound settings.
- Reselect the headphones. Click Control Centre in the menu bar, click Sound, choose the Mac's internal speakers, then choose the headphones again.
The second step is easy to miss.
Headsets that switch devices
AirPods and some other headsets connect to several of your devices and can move between them by themselves, for example to your iPhone when a call rings. When that happens during a Mac call, the Mac's output, and its input if you were using the headset's microphone, changes under you. Using the Mac's own microphone limits the damage, because it does not move. When your Mac switches audio devices mid-call covers the settings that control switching.
What it means for transcripts
A speech recogniser works from the sound it is given. A voice squeezed through call mode has less detail, and recognisers make more mistakes on it, starting with names and numbers. If your side of a transcript is noticeably worse on days you wore a Bluetooth headset, this is the likely reason. Getting better meeting transcripts covers the other causes.
Recording with a Bluetooth headset and Notey
Notey records the input selected in System Settings › Sound as your side of the meeting and what your Mac plays as the other side. So the choice above decides what Notey hears too:
- Headset for listening, Mac microphone for speaking: your side is recorded from the Mac's microphone at full quality, and the other side is captured from what the Mac plays, wherever it plays it.
- Headset for both: your side is recorded in call mode, with the reduced quality described above.
Either way, headphones keep the other side's voices out of your microphone, which keeps them off your side of the transcript. Setting up your Mac's audio for calls covers the rest of the setup.
Frequently asked questions
Why do my Bluetooth headphones sound bad when I join a call on my Mac?
Joining the call opened the headset's microphone. The headset switched from its listening mode to a two-way mode that carries lower-quality sound. Apple describes this in its support article on reduced Bluetooth sound quality.
Which Bluetooth codec does my Mac use?
It depends on the headphones and which mode they are in. System Settings does not name the codec. What you can control is whether the headset's microphone is in use, which decides the mode.
How do I keep high-quality sound on Bluetooth headphones during a call?
Choose a different microphone, such as the Mac's built-in one, under System Settings › Sound › Input and in the call app. The headset stays in its listening mode because its microphone is not open.
Why is my Bluetooth sound still bad after the call ended?
Something may still be using the headset's microphone. Apple suggests quitting apps that use it, closing the Sound settings, and selecting the Mac's speakers and then the headphones again in Control Centre.
Does this affect call recordings and transcripts?
Yes. A recording of your voice through a headset microphone in call mode carries the same reduced quality, and recognisers make more mistakes on it.
Are newer AirPods better for calls on a Mac?
Newer headsets and newer versions of the Bluetooth standard have narrowed the gap, but the two-mode design is the same. Using another microphone for speaking avoids the switch on any headset.