Depends on what you want to do with your audio CDs, the player you're gonna use, and your expectations in terms of audio quality...
Best audio quality is achieved from regular PCM files, i.e. WAV (or AIFF for Mac) files. There are other PCM formats but you won't meet them quite often.
Many people burn from MP3 files and don't hear the difference when the bitrate is high (over 192kb/s). I do :bigsmile: (hear the difference)
If you only have MP3s, converting them to WAV files before burning won't improve audio quality whatsoever.
It's also possible with some CD players to play a data disc with MP3 files. Check the manual of your CD player.
Hope this helps