Symptoms: Audacity is unable to get any input from the audio output or microphone. System uses PulseAudio and ALSA.
The problem seems to be in Audacity’s input picker. The solution is to use the Pulse Audio Volume Control to pick the application’s input.
The way to implement the solution is to run the PulseAudio Volume Control app, pavucontrol, before you run Audacity. The PAV will take over the inputs, and give you control of the inputs to Audacity.
PAV acts like an audio mixer.
To Record Audio Output Mix to Audacity
Start PulseAudio Volume Control
Start Audacity
In Volume Control, Input Devices Tab, at bottom “Show: All Input Devices”
Unmute “Monitor of…” and set the level to 100%.
(You might as well unmute all of them.)
In Audacity, start recording.
In Volume Control, Recording tab, ALSA plug-in, set Capture from to “Monitor of…”
The recording should show the mix.
To Record USB Microphone (Blue, Samson, Zoom) to Audacity
Start PulseAudio Volume Control
Start Audacity
In Volume Control, Input Devices Tab, at bottom “Show: All Input Devices”
Unmute “Blue… and set the level to 100%.
(You might as well unmute all of them.)
In Audacity, start recording.
In Volume Control, Recording tab, ALSA plug-in, set Capture from to “Blue…”
The recording should show the mic signal.
To Run Two Copies of Audacity
Install the regular Audacity and the Audacity Flatpack.
You can now execute each independently.
In Volume Control, Recording tab, you can see two Audacity ALSA plug ins entries. Inputs to each are controlled independently.