Prenasalized stops or consonants are phonetic sequences of nasal plus plosive that behave phonologically like single consonants. That is, like affricates, the reasons for considering these sequences to be single consonants is in their behavior, not in their actual composition. However, there may also be phonetic correlates which distinguish prenasalized consonants from other sequences of nasals and stops.
The Bantu languages are famous for their prenasalized stops (the "nt" in "Bantu" is an example), but similar sounds occur across Africa and around the world. Ghana's independence hero Kwame Nkrumah had a prenasalized stop in his name, as does the capital of Chad, N'Djamena (African prenasalized stops are often written with apostrophes in Latin script transcription although this may sometimes indicate syllabic nasals instead). An example of the unitary behavior of prenasalized stops is provided by Fijian. In this language, as in many in Melanesia, there is a series of voiceless stops, , and a series of prenasalized stops, , but there are no simple voiced stops, . In addition, Fijian allows prenasalized stops at the beginning of a word, but it does not allow other consonant sequences. Thus the prenasalized stops behave like ordinary consonants.
When Tok Pisin is spoken by people in Papua New Guinea who have similar phonologies in their languages, voiced consonants are prenasalized. For example, the preposition bilong (from English belong) is pronounced [mbiloŋ] by many Melanesians. The prenasalization behaves as a phonetic detail of voicing, rather than a separate segment.
In dialects of northern Japan, standard voiced stops are prenasalized, and voiceless stops are voiced. For example, /itigo/ "strawberry" is [itɕigo] in most of the south, but [izɨŋɡo] in much of the north.
Prenasalized stops are also found in Australia. The Eastern Arrernte language has both prenasalized stops and prestopped nasals, but does not have any other word-initial consonant clusters. Compare [mwarə] "good", [mpwaɻə] "make", [pmwaɻə] "coolamon".
Sri Lanka Malay has been in contact with Sinhala a long time and has also developed prenasalized stops. The spectrograms on the right show the word gaambar with a prenasalized stops and the word sambal with a sequence of nasal+voiced stop, yet not prenasalized. The difference in the length of the [m] part is clearly visible. The nasal in the prenasalized word is much shorter than the nasal in the other word.
This phonetic information is complemented by phonological evidence: The first vowel in gaambar is lengthened, which only happens in open syllables in Sri Lanka Malay. The syllabification of gaambar must be gaa.mbar then, and the syllabification of sambal sam.bal.