Turn off audio loopback from microphone

The link in your question disables the mic, and in my case it even didn't help, the mic became disabled for applications, but the echoing stayed. What I've done to solve this:

1. Open alsamixer in terminal.

2. Press F3 to make sure you are on the playback tab.

3. Find any interesting setting there for "Mic" or "Capture" which shouldn't be there, since we are on the playback tab.

4. Either mute that volume meter by pressing M or lower its level to zero with the cursor keys.

   Now it shouldn't echo back, and recording with the mic should be also possible.

5. If it still echos back, then you have to mute the mic volumes, just go back to alsamixer press F4 and mute what you have to on the capture tab.

For anyone facing this, I had same issue in Ubuntu 18.04, and was resolved by changing Settings -> Sound -> Output -> Profile (drop down selection) and used 'High Fidelity Playback' instead of 'Headset Head Unit'