quick and dirty audio amp?

[Linux for blind general discussion]

I would like sometimes to use my pc to amplify audio; my hearing is very porr.
I would like to just have the mic or line-in amplified and come to my headphones.
I used to know how to do this but cannot remember.
Can you suggest the easiest way using command-line command?
Ubuntu 16.04lts, x86/64 with alsa and many audio programs on there.
thanks.