RipperX is  a GTK program to rip CD audio tracks and encode them to the Ogg, MP3, or FLAC formats.

To get MP3 file from an audio CD RipperX need an other tool: lame.
LAME is a high quality MPEG Audio Layer III (MP3) encoder licensed under the LGPL.

The problem with RipperX is that it ignores if the command ‘lame’ is not present in the machine.

The result is an empty MP3 file.

To solve this just install lame (with aptitude, apt-get …)