with traditional normalization, audio progs scan a file for the loudest peak and amplifies so that the peak attains the loudest level.
but if you do it while mastering, the songs will still vary in level because our ears respond to a songs "average" level. Metanormalize(wavelab tool) normalizes using RMS(average levels)
WAVELAB:
drag all the files into the main window.
select batch process from the tools menu
click on the input tab, then add file button in the batch processing window, then select ADD ALL.
click on the edit batch plug ins button, when the processor list appears open the plug ins folder, and double click the Meta Normalizer plugin.
after clicking on the meta normalizing plugin, it appears in the left column in the processor list. double click to show the meta normalizer parameters , click on "equalize loudness"(RMS) "check global"(check maximize if possible if you want to use every bit of headroom)then check ok.
click on the processor list OK button
click on the batch process output tab. Click on the folder button to navigate to the desired folder, or create a new one. click on RUN and the files will be metanormalized and deposited where you want...