Realtek Digital Output bypasses the translation process inside your computer. Instead of converting the signal to analog, the computer sends the raw digital audio data out through a specific port (usually the yellow/orange RCA jack or an Optical S/PDIF port) to an external device.
This is the most common issue. If you do not have a device plugged into the digital output port (Optical or Coaxial), your computer is sending audio into a void. what is realtek digital output