If you are tired of looking for effective audio converters for Ubuntu, I recommend that you try Gnac. This audio converter is designed to work under the GNOME desktop and it can convert audio files between all GStreamer supported formats.
To install Gnac on Ubuntu 11.04/10.10/10.04, run these commands via the Terminal:
sudo add-apt-repository ppa:gnac-team/ppa
sudo apt-get update
sudo apt-get install gnac