In-game Voice Chat with Built-in Mic
In-game voice chat is supported through the built-in mic. The built-in mic can be muted/un-muted by pressing the TX button when the adapter is paired with a headphones.
The built-in mic has an effective operating range of 4ft or less, its main purpose is for in-game voice chat in handheld mode. It will not be practical for docked mode operation as the user will most likely be more than 4ft away from the adapter.
Under normal usage, Bluetooth headphones is only used for receiving audio from the Switch, mic on the Bluetooth headphones is not enabled by default. If you intend to do in-game voice chat in docked mode, there is a beta feature, HFP mode, that allows voice chat through the headphones mic.
In-game Voice Chat with Headphones Mic (HFP Mode)
1) Turn on the Switch and go to the Home menu.
2) Press and hold the left button (TX) while inserting the adapter into the Switch.
3) Keep holding the left button until the LEDs light up after inserting the adapter.
4) Connect with headphones as normal.
Once HFP mode is enabled and adapter is connected with headphones:
1) You can still press TX to toggle the built-in mic. Internal Mic Mute LED off indicates built-in mic is not muted, Internal Mic Mute LED On indicates built-in mic is muted.
Or
2) You can press the Play/Pause button on the headphones to toggle the headphones mic. aptX LED flashing indicates headphones mic is On.
HFP mode will be disabled automatically once the adapter is unplugged from the Switch or when the Switch goes into Sleep/Off mode.
Note: HFP mode is still in beta and it doesn't work with every Bluetooth headphones on the market. In addition, audio quality is degraded when headphones mic is turned On.