To find out if a package is installed, you can try this in the command line:
dpkg-query --status aldo
If you want to search among the packages that currently ARE installed, try this:
dpkg-query --search aldo | less
This will list all packages that have "aldo" in their descriptions or names. The '| less' part makes it show them in a scrollable list. Try typing 'man dpkg-query' and 'man less' to get more information on these commands.
I'm glad you worked out your sound problem.