Ubuntu – Microphone not working on 18.04 for any web or desktop conference app: No one can hear me

I've had weird problems where the mic was muted and I had to use pavucontrol to unmute it. You can install the additional pulseaudio utilities:

sudo apt-get install paman padevchooser paprefs pavucontrol pavumeter

Check the input tab in pavucontrol and make sure its not muting your mic. You can also play with the configuration tab in case that is wrong, but note your initial setting first.

Keep in mind what arochester and Joao are saying, make sure pulseaudio is selected in the skype audio options.

Solved with pavucontrol. I had already tried the pulseaudio volume control, but you need to do a particular thing to make it work.

First, install pavucontrol:

sudo apt-get install pavucontrol

Then start it:

pavucontrol

You'll get the volume control window. Now, you could go to "Input devices" and select the webcam microphone as your input source: THIS WON'T WORK. This is how you do have to it:

• Click on the "Recording" tab. This tab shows the applications that are capturing audio in that very moment, so it will probably be empty.
• Start skype then call the Echo / Sound Test Service (or anyone you like who will answer)
• When the other party answers, Skype begins capturing audio and will be shown in the "Recording" tab of the pulseaudio volume control window
• From the "Input from" drop down list, select your webcam

And voilà, you'll get your microphone back.

Alternatively, as described in SkypeTroubleshooting

• [..] go into the Skype Options menu - Sound Devices
• remove the tick at: Allow Skype to automatically adjust my mixer levels.
• Click Apply.
• Readjust the sound mixer controls (pavucontrol input devices will work now).

This worked fine for me.