At Partners In Rhyme we deliver all of the audio our customers order in WAV format. Some of our customers need their audio in MP3 format and we help them with instructions on how to easily convert their audio to any format they need using free iTunes software.
For those of your who do not want to download software to convert your audio there is a new free online audio conversion site just for you called Media.io
http://media.io/

To convert using iTunes follow the instructions below:

Converting to MP3 is very easy. If you don’t already have it download the free app iTunes (Mac or PC) here:

http://www.apple.com/itunes/download/

Load all of the sounds into iTunes (simply drag and drop in most operating systems) then choose iTunes > Preferences
Click on the ‘General’ tab, then click on the ‘Import Settings’ button and choose ‘MP3 Encoder’.
You can also choose the quality setting you want or choose ‘custom’ if you have a specific setting in mind.
Click OK. Then go back to the library, select all of your tracks that you want to convert, then choose Advanced > Create MP3 Version.
Once that is done you will have an MP3 version of the track in your iTunes music folder.