In short, in Ubuntu 12.04, if you get “unable to load typewriter sounds” in Focuswriter, open a terminal and enter “sudo apt-get install libsdl-mixer1.2-dev” (if you try “libsdl-mixer1.2” you will get package not found).

Focuswriter (sudo apt-get install focuswriter) is a full-screen tool in Ubuntu for distraction-free writing.

http://flattr.com/thing/417372/FocusWriter-1-3-0-Released-Distraction-free-writing-on-Ubuntu You can theme it like so, though I prefer the console-like green on pure black, monospace font.

What I really like is the typewriter sound effects (it helps me concentrate & feel productive instead of despairing over my papers). I got the typewriter sounds working in 10.04 through some magic I’ve forgotten. Now I have a clean install of 12.04 on my netbook, but when I went into Settings > Preferences > check Typewriter sound effects > Ok, it said “unable to load typewriter sounds”.

http://gottcode.wordpress.com/2011/06/27/even-more-bugs-fixed-in-focuswriter/#comment-276
@Lito: You need to install the package libsdl1.2-mixer to get typewriter sound effects because they are now fully optional.

Okay… so I try “sudo apt-get install libsdl1.2-mixer” but get package not found. https://bugs.launchpad.net/ubuntu/+source/focuswriter/+bug/897055
According to this bug report, it should just magically be fixed. And according to ubuntu.com, this package is in Precise.
Turns out the package is actually called “libsdl-mixer1.2-dev” for ubuntu. So “sudo apt-get install libsdl-mixer1.2-dev” and yay typewriter sound effects will load.

If you get a package not found error, run “sudo apt-get update” to make sure you have the latest packages. If you still don’t see it, Ubuntu Sofware Center > Edit > Software Sources and make sure all the sources under “Ubuntu Software” and “Other Software” are checked.