I have an audiotechnica at2020 usb and the astro a40s with mixamp. how do i record both at the same time via USB
Audacity 2.0.5
Windows 8
There might be a way to do it, but typically you can only record from one “device” at a time.
Assuming they can both speak the same data language (44100, 16-bit mono), you can create an Aggregate Device.
Go > Utilities > Audio MIDI Setup.
Aggregate Device will smash your two devices together to look like one without regard to syncing them. That’s why it asks you which device you want to sync to, because the other one is going to drift off lip sync. You can’t stop it. Your two microphones have different electronics and don’t “know” about each other. If you keep your shows short, you should be OK.
You can do a sync test. Start recording and clap loudly. come back in an hour and clap again. Measure how far apart the two claps are at the end.
You can’t split the two performances. They’re married.
Koz
Thanks everybody for the help
Not on Windows 8, you don’t 
- that’s for Mac OS X.
See Audacity Manual . I think you can aggregate with Virtual Cables (donationware) too - you would need VB-CABLE A as well as VB-CABLE.
Be aware of the issues synchronizing two different devices with different clock speeds.
Gale
Oops. You have the wrong computer.
Koz