My bet is that is not really about audio quality, but because in order to understand speech you need to fully understand the language. Try to write down something you hear in a foreign language. As someone who has learnt English as a foreign language I can assure you that at first I wasn't able to even separate between words, it just sounded as a continous stream of sound. Once you learn enough vocabulary you identify some words. Once you identify enough words you are able to fill the gaps using the context. With practice the whole process happens so fast you don't even notice.
