For the typical Windows Sound Mixer, or whatever it's called,...
["Volume Control"], there is a little speaker icon on the taskbar.
Double click this speaker icon, and a "mixer" control should pop up. By default, this is the "playback" side of the mixer.
Click "Options", then click "Properties", and a 'properties' window should then pop up, displaying a "playback" and "record" option.
Now, click on "Record", and that sets the virtual mixer to control the "record" side. Now, click "Ok", and you should now be displaying the "Recording Control" side of the 'sound mixer'.
On this, [Recording Control screen], you then check "Line", and then set the level,... for "Line IN", i.e. the input/recording side of the virtual-mixer.
Depending on the audio source, I find that a "Line IN" setting of about "4" is ideal, but you may have to experiment with setting the levels, for best results.
Try that.
