Your earbuds sound great with music. Then a call starts, and both the call and anything else that is playing turn thin and muffled. Nothing is broken. You are hearing Bluetooth change modes.
Two profiles, one link
Classic Bluetooth audio works through profiles, sets of rules for a job. Two matter here:
- A2DP, the Advanced Audio Distribution Profile, streams high-quality stereo in one direction, from your phone or computer to your ears. It doesn’t carry the mic.
- HFP, the Hands-Free Profile, and HSP, the Headset Profile, carry audio both ways so the mic can work. Microsoft says HFP plays audio in mono, one channel in both ears, at lower fidelity than A2DP. Sennheiser explains why the sound drops: in the call profile, part of the link’s bandwidth goes to the mic.
The moment an app opens the headset’s mic, the headset leaves A2DP for HFP. Microsoft’s own example is a racing game: join a party chat, and the game’s sound drops from stereo to muffled mono.
Why HFP sounds like an old phone
Microsoft points out that classic Bluetooth audio was designed more than two decades ago, when flip phones and bulky earpieces were the state of the art. Its original codec, the scheme that compresses the audio, supported only an 8 kHz sample rate. A digital signal can only carry frequencies up to half its sample rate, so 8 kHz audio stops at about 4 kHz. Microsoft says that leaves out nearly all the treble and sounds a little worse than AM radio.
| Mode | Sample rate | Audio up to about | Stereo with the mic on |
|---|---|---|---|
| HFP, original | 8 kHz | 4 kHz | No |
| HFP, wideband | 16 kHz | 8 kHz | No |
| LE Audio, super wideband | 32 kHz | 16 kHz | Yes, on Windows 11 PCs that support it |
| A2DP | Music quality | Music quality | No mic at all |
Windows 11 and most modern headsets support wideband voice, which doubles the rate to 16 kHz. Even so, Microsoft says wideband is still closer to AM radio than to the CD-quality sound the same headset gives you when its mic is off.
LE Audio changes the rules
LE Audio is the newer Bluetooth audio system, built on the Bluetooth Low Energy radio. The Bluetooth SIG says it brings a new codec, LC3, which in listening tests sounded better than the classic SBC codec even at half the bit rate. More to the point for calls, LE Audio replaces A2DP and HFP with profiles that handle media and voice together. For headphones and earbuds that profile is TMAP, the Telephony and Media Audio Profile, and Microsoft says TMAP requires super wideband voice at a 32 kHz sample rate.
On Windows 11, an LE Audio headset can now keep stereo while its mic is on. You need all of this:
- Windows 11 version 22H2 or newer for LE Audio, and the latest updates to version 24H2 for super wideband stereo
- A PC whose Bluetooth radio, audio codec and drivers support LE Audio; Microsoft notes that a PC marketed as supporting Bluetooth LE may still not support LE Audio
- A headset whose maker lists Bluetooth LE Audio or the TMAP profile
- Use LE Audio when available switched on, under Settings → Bluetooth & devices → Devices; if the switch isn’t there, the PC doesn’t support LE Audio yet
What to do today
- Use a different mic. If the earbuds only play the call while your computer’s mic or a USB mic picks you up, the headset’s mic stays off, and Microsoft’s description of the switch says it is the mic that triggers HFP.
- Use a wired or USB headset for calls that matter. Zoom suggests a USB headset when Bluetooth gives trouble, and notes that a USB adapter can work better than native Bluetooth.
- Connect to one device at a time. Zoom warns that Bluetooth headphones may not work properly when they are connected to several devices, and that you may hear others while they can’t hear you.
- Check which mic the app uses. Google notes that a headset may end up using the built-in mic, and that some Bluetooth headsets work well for ordinary calls but poorly with Meet.
- On AirPods, check the mic setting. If Microphone is set to Always Left or Always Right, Apple says that earbud stays the mic even when it is out of your ear or in the case.
- Turn on LE Audio if your PC and headset both support it.
Recent AirPods, the AirPods 4, AirPods 5, AirPods Pro 2 and AirPods Pro 3, also offer Voice Isolation during calls, which Apple says removes background noise such as wind for the person you are talking to.
See it in the test
In the noise test, pick the headset as your mic, read the sentence and watch the spectrum, which runs up to 8 kHz. In the original 8 kHz call mode, everything above about 4 kHz stays dark. Then switch to a wired mic and compare.