I've been dabbling recreationally in a few languages, checking their phonetic repertoire, and one thing that's making me very confused is my apparent inability to tell nasalized sounds apart from the non-nasalized ones. For instance, Portuguese with its nasalized vowels is giving me major problems, since it's often the case that nasalization is a minimal pair (for example, to me "avó" sounds exactly the same as "avõ"). And Mandarin Chinese has the distinction between final "n" and "ng", again, often a minimal pair, so to me "mēn" sounds exactly like "mēng". At least in English there's not such a reliance in minimal pairs between "n" and "ng", and you can make do pronouncing /ŋ/ as a separate /ng/, or even a plain /n/ for -ing verb endings. Is my problem too unusual? (Couldn't find any data online on difficulties hearing them apart, only on difficulties pronouncing them correctly.) And can I do anything to help me tell them apart more reliably?