To install Skype, it is preferable to use the Ubuntu repository, which will install everything needed to manage sound and video properly.
If you take the package available on the official website, it is likely that the sound will not be managed properly.
1 – Install Skype:
sudo add-apt-repository -y ppa:andykimpe/skype && sudo apt-get update
sudo apt-get install skype
2 – Install the wrapper:
sudo add-apt-repository ppa:skype-wrapper/ppa
sudo apt-get update && sudo apt-get install skype-wrapper