I know. Lots of people have this issue. I have spent most of the last 12 hours searching for a solution that works for me. I hope someone here can help.
I have a Dell Studio 540 Desktop. The sound card appears to be on the motherboard and Device Manager calls it Realtek High Definition Audio. I have attempted to download and install the latest driver, but I am not sure it has changed from when I started. I appear to be at 6.0.1.5864. I have a cable connected to the line-in and the amplifier of my old stereo. I want to record some tracks from vinyl that I cannot get anywhere on digital media.
I am on Windows 7 x64 SP1 and Audacity 2.0.5.
I can see line-in in my Windows Sound Recording Devices. Through the process of showing and enabling devices, I can now also see Stereo Mix. I have tried both of them enabled and default, using both Windows and the Realtek HD Audio Manager. In both cases, I can hear music played on the turntable playing through my computer speakers, but I can get neither to be the input source in Audacity. Here’s what I get in Edit Preferences Devices:
Interface
Host: Windows DirectSound (MME is not listed in the drop-down)
Using: PortAudio V19-devel (built Oct 18 2013 22:37:53)
Playback
Device: Speakers (Realtek High Definition Audio)
Recording
Device: No devices found (I have never seen any other items in this drop-down list)
Channels: 2 (Stereo)
I have re-scanned devices, stopped and re-launched Audacity, rebooted several times, enabled and disabled various devices, tried it with exclusive settings checked and unchecked, matched the bit rates channels and depth, shouted and cursed, and read many glowing reports of people successfully doing this after changing something that won’t fix mine.
I await a reply with high hopes…
Here is from the Audacity manual:
choose the Windows WASAPI host (in the first box in Device Toolbar) and then the (loopback) input in the Input Device box. Choose the loopback input for the computer sound device you will be listening to (for example, “Speakers (loopback)” ). The loopback input records computer playback even if your sound device lacks its own stereo mix or similar input.
Thank you so much! I had read something fairly early on that told me NOT to use WASAPI, so I was blowing right by that in the manual. I also had to check “Listen to this device” on the Listen tab of the Line In device in Windows Sound. Before I did that Audacity would not monitor or record anything. I have now successfully recorded, edited, and de-clicked music from vinyl. So happy!
And they were correct, for someone recording vinyl to Line-in of the computer. 
You would want to choose Line-in in Audacity’s Device Toolbar if you could, rather than record playback of that input through the speakers.
Yes. Recording using Windows WASAPI loopback would be much better than if you had used stereo mix (which would add extra digital-to-analogue and analogue-to-digital conversion steps).
But “Listen to this device” can use quite a lot of CPU processing power, so there could be an increased risk of dropouts in the recording. Probably there would be no more risk than using Audacity’s software playthrough, but with your method you are making playthrough mandatory.
That’s just broken, even though you seem to have been doing all the “correct” things to fix it.
That said, the drivers I find for Studio Desktop Windows 7 x64 on http://www.dell.com/support/home/us/en/19/product-support/product/studio-desktop/drivers are “Realtek ALC888 HD Audio, v.5.10.0.5864, A00”.
Gale
Gale, Thanks for your comments. So to minimize the risk of dropouts, should I instead use software playthrough? Or better yet is there a way to get Line In to show as a choice in the input drop-down?
No you should never use Audacity’s software playthrough when recording computer playback.
If you cannot get Audacity to see “Line-in” I think you now have as good a configuration as you can get. The recording should remain digital and should be essentially as good a quality as if you could record Line-in, though you probably won’t be able adjust the input level in Audacity.
You may need to stick to 44100 Hz Audacity project rate when using Windows WASAPI. Other rates may cause distortions on a few machines.
If you did not care about listening while you were recording, there would be a theoretically greater risk of dropouts using WASAPI loopback compared to using Line-in without software playthrough.
I think the pros and cons are as set out above.
If I was you I would be banging on Dell’s door as to why you had no line-in and stereo mix in recording applications. If you turn off “Listen to this device” and make Line-in default in Windows Sound, does Windows Sound Recorder record the Line-in?
Do the “v.5.10.0.5864” drivers change anything?
Gale
I fear they would tell me that I should try it on a computer that isn’t 5 years old! 
Yes, that worked when I tried it before.
I haven’t taken the time to do that yet since this approach seems to be giving me quality that is good enough for my purposes. But if I start to have trouble, I will try that next.
Thanks again.
WASAPI has been turned off in the alpha 2.0.6 - but with WASAPI loopback retained to facilitate recording audio that is playing on the computer.
I tested WASAPI loopback extensively and now use this all the time for my production recordings of webcasts - with excellent results. So my recommendation is use it 
My Tosh laptop (like many modern laptops doesn’t have a line-in) I circumvent that with the use if an external USB souncard - I record from FM radio and I digibitted all my LPs that way - see this sticky thread: Sound Card Reviews
WC
It could be that Sound Recorder is using Windows WASAPI for that recording. WASAPI is only available in released versions of Audacity for loopback recording, not for recording of physical inputs.
But I think your sound device or its drivers are not working correctly.
Gale