Audacity (http://audacity.sourceforge.net/) is freeware audio editing software with spectrum graphs that visualize sounds in a way that gives you one way to compare two different recordings. You can import a sound file, play it and see its graph, then record yourself and place the two graphs next to one another to get a pretty detailed picture of where they differ. Takes a little getting used to doing the interpretations, but might be useful for what you’re trying to accomplish.
That Audacity software is great, with minimum effort and know how i was able to clean up one of the Doegen recordings (http://www.dho.ie/doegen/ ), which was barely audible to only a minor hissing and much clearer sound quality. Youd imagine they would have done something similar or better before they put them online, would they not have access to better sound software and people experienced in such matters?