Does any one know of an application that can convert audio to text? I'm running ubuntu 12.04 LTS.
The software you can use is CMUSphinx. Unlike suggested in another answer Julius is not suitable because it requires models. Models for large vocabulary speech recognition are not available for Julius.
You can use pocketsphinx to convert audio file. Those two commands must do the work. First you convert the file to the required format and then you recognize it:
US English generic acoustic models are available for download on CMUSphinx website
I you are looking to convert speech to text you could try opening up your Ubuntu Software Center and search for Julius
Or another option that isn't in the Software Center is Simon