your daw renders a wav, unless it has an option to render as mp3.
You have the option of converting it via different qualities, much like different wav files.
I think depending on the codec used to convert to mp3, might have some part to play. but i haven't noticed any differences.
I master my tracks in a daw called reaper, i can convert things into what ever file type i want.
itunes also can convert things into an mp3.
it depends on the settings for conversion that would dictate the quality of your mp3.
a person more educated on the matter should correct me. but that's what i've gathered up.
