I have just got a new hp tower with windows 8 pro pack. I think I installed with .exe installer. I have been trying to record the sound coming through my computer. The recording device settings in my computer are Stereo Mix - IDT High definition audio - default drive. My output play device settings are AMD HDMI output payback. I have SKY FM playing through my HDMI going to my tv which then goes through my sound system. Can hear it fine. I start audacity. My settings are MME-AMD HDMI OUTPUT-STEREO MIX (IDT HIGH DEFINATOR) - 2 stereo input. I hit the record. I just see straight lines streaming across the screen. I let this happen for a minute or so and then stop. Then export file as WAV. When I try to play hear nothing? When I list properties of file it shows 43 mb of something. I have tried everything I can think of. Don’t know what I am doing wrong. PLEASE HELP. 
This is where using the instruments comes in handy. If you see no bouncing red recording meters and only get a flat blue wave, then you’re not getting any sound.
http://kozco.com/tech/audacity/Audacity1_record.jpg
What you are getting is several minutes of perfectly recorded silence. Unlike compressed formats, WAV is a minute by minute constant size no matter what’s in the show.
Right click on the red recording meters (make them much larger like mine by dragging the right-hand edge) and select Start Monitoring. That will give you bouncing red meters when you succeed in getting your show into Audacity.
Stereo-Mix should have done it. That’s the device you select to make Windows self-record. It that’s what selected in Audacity Edit > Preferences > Devices > Recording?
Koz
Is that a HDMI output from your graphics card? In that case it is a separate device and has no connection at all to the “Stereo Mix” of the IDT sound chip.
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Ragnar
The HDMI output is from the graphics card but is also the audio output for what comes out of my computer. My knowledge of computers is not what I call high, so I would appreciate any input on what I should be doing.
Yes to KOZ that is what I have set in audacity.
In order to record sounds that are playing on your computer you need to set Audacity to record from “Stereo Mix”, but “Stereo Mix” is on the sound card, not the video card, so it will only record sounds that are playing through the sound card and not sounds that are playing through the video card.
To record what is playing on your computer you need to redirect the audio output of the computer so that it uses the sound card and not the video card. You would do this in the Windows Sound Control Panel.
That was my problem. If I have the play back setting set to speakers/headphones in the computer and the same in audacity it records. That seems to be the only setting that will work. It does not work if I have play back device in computer set to digital audio and the same in audacity or the communications headphones. Should it? Another question I have is how to record the sound from cable set top box. The left and right audio go from the set top box into my graphics card red and white rca jacks. How do I go about getting it to recognize that?