OBS captures desktop audio and microphone by default; a wrong device selection yields a silent stream

OBS Studio defaults to capturing desktop audio and microphone, and you verify this by watching the volume meters move in the Audio Mixer dock. If the meters stay still, either the wrong device is selected or that device is producing no signal; the fix is Settings → Audio, where you pick the devices by name. This is a frequent failure point on systems with an audio interface or virtual audio cable, where OBS may default to a device that is not carrying the sound you want. For a live-coder, desktop-audio capture picks up browser sound (e.g. Strudel in a tab) but may miss a DAW that outputs to an interface OBS is not monitoring.

Examples

Strudel plays through the system default output and OBS’s Desktop Audio is set to Default, so the meters move and the stream has sound. But if a DAW outputs to a Focusrite interface while OBS Desktop Audio stays on Default, the DAW audio never reaches the stream.

Assessment

How do you check that OBS is capturing audio from the right device, and what do you change if the Audio Mixer meters are not moving?