While recording sound, there was too much noise and I changed some settings that I do not remember now and could not find the blog I used for instructions. The only thing I remember was removing pulseaudio and changing some sampling rates

Now I can almost use Audacity to record (it creates some humming only when talking) but I can at least record some sound.

The others: Skype, Google Voice or SFL Phone, I cannot use it at all. I can hear, but my voice is not delivered.

Is there any way to revert all changes I made (like a restore point or as a fallback: reinstalling kubuntu from scratch)

I changed nearly all settings with KMix and alfamixer, but it did not solve my problem.

Do you have any ideas?