Here is the hack for my Dell Inspiron 1520:
A lot of people have been reporting various versions of this issue. In short you are not able to hear line-in audio from the computers speaker even though the meter shows an audio signal. It seems that simply adding a registry key to enable the input monitor will fix the problem, at least it did on my Dell Dimension 9100. Once you add this key and reboot, you will need to enable the input monitor by going to “Control Panel” –> “Sound” –> “speakers/headphones” click on properties, then click on the “Levels” tab and enable the input monitor button.
That should do it, it did for me.
Here is the contents of the reg file I imported to fix the problem:
Windows Registry Editor Version 5.00
You can either create a reg file with this text, or go there yourself and create the binary value.
Here is my standard Microsoft type warning that you should never edit the registry unless you really know what you are doing!
Thanks snashbar very much for his/her post “Possible fix for LIne-in issue with SigmaTel driver in Vista”
P.S. After I solved the Line-in problem, I found that the Line-In is really noisy. I finally found a solution: change the level of Microphone/Line In and Microphone Boost to 0:
P.S.2 For Mac OS X user, there is an application called “LineIn” for you to put through line-in to speaker.