Denasalization
In phonetics, denasalization is the loss of nasal airflow in a nasal sound, such as a nasal consonant or a nasal vowel. This may be due to speech pathology, but also occurs when the sinuses are blocked from a common cold, in which case it is called a 'nasal voice'. (The latter is not a linguistic term.) The symbol for this in the Extended IPA is ⟨◌͊⟩.
When speaking with a head cold, the nasal passages still function as a resonant cavity, so a denasalized nasal [m͊] does not sound like a voiced oral stop [b], and a denasalized vowel [a͊] does not sound like an oral vowel [a].
However, there are cases of historical or allophonic denasalization which have produced oral stops. In some languages with nasal vowels, such as Paicĩ, nasal consonants may only occur before nasal vowels; while before oral vowels, prenasalized stops are found. This allophonic variation is likely to be due to a historical process of partial denasalization. Similarly, several languages around Puget Sound underwent a process of denasalization about one century ago: Except in special speech registers, such as baby talk, the nasals [m, n] became the voiced stops [b, d]. It appears from historical records that there was an intermediate stage when these stops were prenasalized stops [ᵐb, ⁿd] or poststopped nasals [mᵇ, nᵈ]. Something similar is currently happening with word-initial nasals in Korean, where in some contexts /m/ is neither [m] nor [b], but [m͊].