OS: Debian 9 installed on laptop
Gear: Behringer UMC404HD Audio Interface; Analog Mic.

Problem: Microphone plugged into interface will not pick up sound.

What works:
The internal mic on the laptop picks up sound, and the built in speakers output sound.
Currently, headphones are plugged into the audio interface for sound output. This output method works correctly and produce sound.
A Microphone is plugged into the interface, and Debian "knows" that the line is there as "UMC404HD 192k Multichannel" appears in the system sound input settings and the pulseAudio volume control.
This interface/mic combo works on Linux Mint installed on a seperate computer. It also works on Windows 8.1 which is installed on the same laptop that is running Debian.

What doesn't work:
Although Debian detects the multichannel input and the multichannel input is selected as the input method to use by default, the sound will not record. For instance, when speaking into the mic while the volume control panel is open, the meter displaying input will not budge, and the voice can not be recorded on any recording or communication software. Muting the internal microphone doesn't help either.

Wondering if anyone with experience with Linux sound can help or direct me in the appropriate troubleshooting directions.
Thanks for reading Much appreciated

Try alsamixer. Disable the internal mic and make sure the external mic is not muted. And why do you want multichannel input? A mic is single channel.

What recording software are you using? Have you tried Audacity?

Hey thanks for the input, though i kind of figured this out just by wrestling with the settings (and switching from Gnome to KDE).

It's a multi-channel input because the mic is running through an audio interface with multiple analog inputs - mainly use if for recording music, but also as a mic while talking online/gaming.

I'll post pics of my sound setting set-up in case anyone has a problem with an interface or mic in the future.

Not sure how many of these are relevant to solving the issue, but here ya go to anyone interested.

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