What is the 'Sound Settings' program's name in Ubuntu

In GNOME audio settings are controlled by the GNOME Control Center

gnome-control-center sound

GNOME is not installed by default in Xubuntu. You can access audio settings by installing the package pavucontrol for controlling sound settings without GNOME dependencies:

I believe that Sound Settings is a part of gnome-control-center. Whenever I open sound settings and run killall gnome-control-center (This command will kill the process requested), it closes my Sound Settings.

I don't know what program you were using before, but you can easily find out what what programs are readily available to you to this sort of thing type apropos mixer or apropos mix at the command line. In my case it pops up a list of two:

• alsamixer
• amixer

The first one, alsamixer, is a mixer that works from the console and offers a lot of functionality. Check the man page man alsamixer to figure out the key bindings.

Another option is to search for 'mixer' in available packages, but that will only work if the mixer has a package of its own, not packaged with other desktop tools: apt-cache search mixer | grep mixer -i --color

Maybe you are able to find out which mixer you were using by browsing through the /var/log/dpkg.log, grep -i mix /var/log/dpkg.log*