When I record new track with stereo mix listening to other existed track,
the result is new track and exited track too.
I wanted only new sound not exited contain but listen.
I have only one PC so I can’t simply connecting with mic.
I tried third party ‘virtual audio cable’ but how should I change the setting?
“Stereo Mix” records everything that is playing through the sound card - that is what it is designed to do.
Windows does not support per application recording with standard Windows drivers.
For support using Virtual Audio Cable, please see the help on their web site http://software.muzychenko.net/eng/vac.htm
Virtual Audio cable is not our software and we are unable to offer technical support for it.
What are you actually trying to do? We may be able to suggest an alternative approach if we know what you are trying to do.
Thanks for the reply!
What I want to do is multi-track recording. Track 1 is no problem. this is MP3 source. Problem is track 2, I wanted to play some musical instrument application while listening to mp3 (track 1) and record it as track 2. I want to listen to both of track 1 and 2, but want to record only track 2. When I set recording source setting as stereo mix, I got track 2 as some application sound + audacity own sound. This is problem.
Although maybe I can record the musical application from other computer with mic, I want to record with only my PC if possible coz I have only one PC.
or Must we still have “physical machine” like 8-track recorder set even in 21st century?
Unfortunately you can’t do that on Windows without ASIO (or possibly Virtual Audio Cable) because the Windows sound system does not support per-application recording. Audacity cannot be distributed with ASIO support due to licensing restrictions, so unless you build Audacity from the source code you are out of options on Windows. You can do this on Linux, or on Windows with some programs that support ASIO such as Reaper, Cubase, Sonar and others, otherwise you need more hardware.
OK, I see…
I’m gonna look for ASIO issue.
Thanks a lot, steve! 
So how you do you record a specific application (but excluding other applications that are also playing sound) on Linux - JACK? If so would this work on Windows? All I see on JACK for Windows are generic system capture inputs, plus it sees Audacity as “PortAudio”. I can’t see any way to click to link outputs and inputs in the JACK patchbay. So with my lack of experience with JACK, all I can make Audacity record is both the Audacity track and audio application playback combined.
Do generic ASIO drivers like ASIO4all provide a per-application patchbay? I didn’t think they used to, in which case ASIO won’t help in Audacity even if you compile it with ASIO support.
Gale
Yes, I’d do it with Jack.
To record from one specific (jack aware) application and not others: Start the application and check that it is using Jack, then rescan audio devices in Audacity (Transport menu). The playback application should now be available as a recording input in the Audacity Device Toolbar.
To record multiple applications simultaneously in Audacity (but not others), you can use an intermediary “dummy” application such as Jack Rack. After starting Jack Rack, use “Rescan Audio Devices” in Audacity, then set Jack Rack as the recording input. Multiple audio applications can then be run and connected to Jack Rack. QJackCtl (Jack Control) includes a patch bay and a connection kit for setting up the routing between applications, though for Audacity you should generally use the Audacity Device Toolbar as Audacity does not respond well to being controlled by QJackCtl.
No I don’t think so, but some ASIO applications have routing options for their inputs and outputs that may allow Audacity to be specified as the output connection. I’ve not used Audacity with ASIO so I don’t know how flexible it is. Other ASIO software (such as most DAW applications) have some means of recording multiple synths and sound modules.
Here’s an example set-up recording Hydrogen drum machine and ZynAddSubFX synthesizer simultaneously into 4 separate tracks in Audacity with real time effects.
(no special sound card required - I’m just using a Behring UCA-202)
Normally I’d not have the screen so cluttered but would have each application set up on a separate virtual desktop.
And here is a really short clip from what was recorded: