# Bluetooth audio: codecs, LE Audio and where the latency comes from

> Why one headset sounds fine in a call and bad in a game, what LE Audio changes, and what Windows actually controls.

**Tested on**

- Build: 26300.9457
- Edition: Pro (26H2)
- Architecture: x64
- Evidence: E1
- Verified: 2026-10-29

## The short answer

A Bluetooth headset usually exposes **two audio endpoints**:

| Endpoint | Profile | Quality | Latency |
|---|---|---|---|
| **Stereo / headphones** | A2DP | good (codec-dependent) | 150–300ms |
| **Headset / hands-free** | HFP/HSP | narrow-band, mono | lower, but sounds like a phone call |

Windows picks the hands-free endpoint when an app opens the **microphone**. That is why music sounds fine, then a Teams call starts and everything sounds like 1998 — the device switched profiles, not "the drivers broke".

## Check what is active

```powershell
Get-PnpDevice -Class AudioEndpoint | Select-Object FriendlyName,Status
Get-PnpDevice -Class Bluetooth | Select-Object FriendlyName,Status,InstanceId
Get-CimInstance Win32_SoundDevice | Select-Object Name,Manufacturer,Status
```

In **Settings → System → Sound**, the output selector shows both endpoints for the same headset. Choosing "Headphones" restores stereo — until an app grabs the mic again.

## Codecs: what Windows decides and what it does not

| Codec | Who chooses | Notes |
|---|---|---|
| **SBC** | mandatory baseline | works everywhere, mediocre |
| **AAC** | device + Windows support | better on supported hardware |
| **aptX / LDAC** | device + OEM stack | often vendor-driver dependent on Windows |
| **LC3 (LE Audio)** | LE Audio stack | newer, lower latency, better battery |

Windows does not expose a codec picker in Settings. What you get is negotiated between the adapter, the Windows Bluetooth stack and the headset. If a vendor ships an enhanced stack, its control panel may show the active codec — the Windows UI will not.

> **Caution: Do not judge Bluetooth latency by a single app**
>
> Lip-sync offset in a video player is often the player compensating; a game's audio latency is the engine's buffer. Measure the device, not the app — and compare wired vs wireless on the same content.

## LE Audio: what it actually needs

LE Audio (LC3, Auracast) requires **all three**: a Bluetooth adapter with LE Audio support, Windows support on that build, and a LE Audio-capable headset. Missing any one and the device falls back to Classic Audio — same headset, same cable-free convenience, worse battery and latency.

```powershell
# adapter and its driver
Get-PnpDevice -Class Bluetooth | Select-Object FriendlyName,Status,InstanceId
Get-CimInstance Win32_PnPSignedDriver | Where-Object DeviceClass -eq 'BLUETOOTH' |
  Select-Object DeviceName,DriverVersion,DriverDate
```

## The real causes of "bad Bluetooth audio"

| Symptom | Cause |
|---|---|
| Sounds like a phone call during meetings | hands-free profile active (mic in use) |
| Stutter when the mouse moves | 2.4GHz interference — the adapter shares the band with Wi-Fi/USB3 |
| Latency in games only | A2DP buffering; no low-latency codec negotiated |
| Volume much lower than wired | absolute volume / device gain mismatch |
| Drops when the laptop lid closes | adapter power management |
| Works, then disconnects every 10 min | power saving on the adapter or the device |

Fixes that work, in order: move the adapter away from USB 3 ports and the Wi-Fi antenna, disable "Allow the computer to turn off this device to save power" on the Bluetooth adapter, and stop apps from holding the microphone open when you are not in a call.

## Related

- [USB devices that are not recognised](https://winbook.fyi/en/windows/peripherals/usb-device/)
- [Touchpads, pens and Precision drivers](https://winbook.fyi/en/windows/peripherals/touchpad-pen/)
- [Printing and scanning](https://winbook.fyi/en/windows/peripherals/printing/)

## Lab boundary

E1. Bluetooth profiles and codec negotiation are documented by Microsoft and the Bluetooth SIG. The lab has no Bluetooth radio, so no codec or latency measurement was made.

## Sources

- [Microsoft Learn — Bluetooth devices](https://learn.microsoft.com/en-us/windows-hardware/drivers/bluetooth/)
- [Microsoft Learn — Audio devices](https://learn.microsoft.com/en-us/windows-hardware/drivers/audio/)
- [Microsoft Learn — HID architecture](https://learn.microsoft.com/en-us/windows-hardware/drivers/hid/)

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Source: https://winbook.fyi/en/windows/peripherals/bluetooth-audio/