I assume that you have headphones and a separate mic.
If so...
Go to Windows sound (right click on the volume icon in the lower tray)
- Default Playback should be your headphones, not speakers. Using speakers is not advised because your mic is going to capture your speaker output and you will get horrible echo.
- Default Recording should be your mic
In OBS Audio:
- Set Sample Rate to be in sync with all your audio devices' format rate (Advanced tab, Default format)
Use the lowest common denominator of all your audio devices.
- Desktop audio should be your headphones
- Mic/Aux should be your mic
In OBS Advanced Audio Properties (right click on any wheel in the mixer):
- Mic/Aux should be set to Track 1 and Monitor and Output
- Desktop Audio should be set to Track 2 and Monitor and Output
In OBS Advanced settings:
- Set your headphones to be the audio monitoring device