Windows fake mic

Such a fake mic exists, and you don't even need code to use it. It's called Stereo Mix, but it may not be available on all sound cards. It works like this:

In the recording devices category, you have two devices: the microphone, and stereo mix.

• When the microphone is the default, if you try to record something you will get sound from the microphone.
• When stereo mix is the default, if you try to record something, you will get the sound that is currently playing on your computer

So, for you to get the desired effect, you would need to set Stereo Mix as the default, and play some music on your computer. The audio is passed internally, and when recording you will get exactly what is playing on your computer. It doesn't make any difference if you speak into the mic, cover it up, or unplug it altogether. You're not even using the mic, you're using stereo mix.

On my laptop, I can enable Stereo Mix from the VIA control panel (the driver for my sound card), or by using the Sound icon in Control Panel.

EDIT: you may need to enable "Show hidden devices" in the Sound applet in Control Panel in order for it to show up (like here)