Devoicing

Devoicing is a phonological process whereby a consonant that is normally voiced becomes devoiced (i.e. unvoiced) due to the influence of a phonological element in its phonological environment.

This process is different from the concept of a consonant being voiceless. The difference is that voiceless consonants are "always" voiceless, whereas a "devoiced" consonant is one that is usually voiced, but which becomes unvoiced under very specific circumstances.

In English

In English, the consonant /m/ (a voiced bilabial nasal) becomes devoiced when it is preceded directly by an /s/ (a voiceless alveolar fricative). Two example of this are the words smack and snack.

Examples in other languages

Another type of devoicing is final obstruent devoicing a systematic phonological process occurring in languages such as German, Dutch, Polish, and Russina, among others. In these languages, voiced obstruents in the syllable coda or at the end of a word become voiceless.