How to loopback audio from one app to another for SDR

Piping the decoded audio from one application to another can be super annoying in linux. Fortunately there is a utility in apt that makes it dead easy (at least on Ubuntu). Simple steps:

• apt install pavucontrol
• start your applications (gqrx/fldigi/direwolf/whatever)
• execute pavucontrol
• In the "Playback" tab, make sure your "output" app is showing up and bouncing the sound meter
• In the "Recording" tab, make sure your "receiving" app is showing up. Click the sound card button and select the "monitor" entry
• Should start working immediately.

For FLDIGI to show up it needs to start recording from the sound card, I had to go to Configure > Sound Card > Audio > Devices > select "PortAudio" > leave capture and playback at "default"