"MP3 Length Baker" will check and bake length of selected MP3 files to new "length" attributes if they are on your XML list. Program checks list by searching the same names as those used at attributes with the url path.
If you want to create simple new XML with structure without attributes for your MP3 files, then you should use Simple MP3 Data Builder (Win).
It works simply - just put exe file there where you have mp3 files and run it. Program will find all mp3 files at this directory and create xml file with all informations in the same place.
If your situation is more complicated and you need to have more freedom you should use DATA Transformer "File List" tool with "Extra DATA" set to MP3.
MP3 Length Baker:
Simple MP3 Data Builder:
DATA Transformer tutorial - jak postavit XML tracklist: