撥音（はつおん）is Japanese nasal sound “ん” [n].
There are three main pronunciations of “ん” (or “ン” in Katakana) though, in general, Japanese people are not aware of the differences. (So, when you ask a Japanese person about the pronunciation of “ん”, s/he may tell you “ん is ん!”)
When the sound after ん is [m], [b] or [p], ん is pronounced as [m].
lips are closed and the tongue touches anywhere)
When the sound after ん is [k] or [g], んis pronounced as [ŋ].
(Your mouth is open and the base of tongue touches the soft palate)
eg. さんがい [san gai] = [ŋ]
When the sound after ん is [t], [d] or [n], んis pronounced as [n].
(The tip of tongue touches the hard palate)
eg. せんたく [sen taku] = [n]
*Uvular [ɴ] at the end of utterances and
*Some sort of nasalized vowel before vowels, approximants (/j/ and /w/), /r/, and fricatives (/s/, /z/, and /h/). Depending on context and speaker, the vowel's quality may closely match that of the preceding vowel or it may be more constricted in articulation. This pronunciation is also found utterance-finally.