The Windows Mixer is confusing.. There are actually two sets of sliders, one for recording and one for playback. The one that pops up initially when you open the Mixer is playback (what comes out the speakers). You need the recording one to set the input that ScannerCast is listening to (as it usually defaults to Microphone).
For XP, open the mixer, then click the Options menu, then click Recording. Make sure the correct sound device is listed in the dropdown box, and under "Adjust Volume For:" select Recording and hit OK. The sliders will change. Make sure the "Line In" slider has a checkmark and its volume is up.
For Vista/7, right click the Volume indicator in the tray (next to the clock) and click Recording Devices. Make sure the Line In device has a green checkmark. If not, right click on it and select "Set as Default Device".
It is very important that you do not select "System Mix" or "What U Hear" as a recording device. This will route system sounds/beeps/etc as well as open mics (headset, webcam, etc) to your feed.
Last edited by KD0TAZ; 08-27-2013 at 7:30 PM..