AT3 to WAV\MP3?

[nothingtosay]

You can use foobar2000 with the vgmstream component as well. It's pretty simple. After foobar is installed and set up and you've downloaded the component, go to File -> Preferences -> Components, click install and point it to where you saved the component. Then add your AT3 files to the playlist, right-click and choose convert. WAV should be the selected output format by default. You can also do a broad range of other formats with custom-tailored interfaces for each codec, provided you've got the command line encoders, so you don't have to use giant WAV files for your lossy AT3 audio. There's a free encoder pack you can use for that.