I suspect it's heavily compressed audio.
His argument is that you'll have a hard time hearing it at all, so if anything's going to help you hear it in the first place, it's garbage in. garbage recordings are the only ones which will survive this test.
Anyway, nobody here is both qualified and willing at the same time to tell you what you need to know about this topic. The article referred to, written by Monty at Xiph, should give you a very good overview of how this works .