Bear in mind that the type of vocal sound that may sound appropriate in opera or operetta very very rarely sounds right in folk song, and that the denigration of "nasal" singing is purely a matter of style - often the result of long exposure to popular music of the 20s,30s,40s,50s,60s and 70s that preferred a different sound. If people say "nasal" to you say "so what" back to them.