Go to terminal and enter
updatedb
This updates the database the following will look through.

Click
Enter the name of the file you are searching for. Pick where to do the
search. In this case "File system". If it is something "you" put in your own
directory area you would pick that. This is not that situation.
Click at the bottom left of the window.

If the file you are looking for has been on your system for sometime the
updatedb command would not be needed. It was done here to make sure the
database is up to date.

pacpl on its own is a script which will only run from the command line.
There are graphical front ends for it, but none of them appear to be
in the standard repositories - and anyway, they all appear to be KDE
only, which isn't a problem if you're running Kubuntu or want to install
all the KDE libraries to run them under Gnome.

As an alternative, you could try Sound Converter, available at
http://www.getdeb.net/software/soundconverter

I've used this in the past and it's OK, but not as powerful as pacpl as
far as I can see.

It's a shame that the front end isn't
easily available. I have now tried pacpl at the command line and it's
very straightforward - still a gui would be nice.

Haven't so far tried soundconverter or winff - maybe later. Gobby: yes,
audacity was my first choice, it's always been reliable, and one of the
things that converted me to Ubuntu in the first place. However I can't
see (perhaps I haven't looked) a batch mode. It's very long winded using
it file by file.

Audacity is a great sound converter and editor. You'll need to install lame with
it for MP3. Very simple to use as well.

Looking in the Ubuntu Software Center I'd say WinFF will do the job
fine and also supports batch conversion. It uses FFMPEG and if you
don't have it the installer should add it in automatically.

Note it says video converter in the information but it does way more
than that - DVD / Audio / FLV / Blackberry Audio etc.. etc.. etc...