Except for voiced nasal followed by homorganic unvoiced obstruent, an unvoiced consonant or sequence of unvoiced consonants in initial clusters immediately preceding a vowel is not itself preceded by one or more voiced consonants.
Standardized
In initial clusters, IF an unvoiced consonant or sequence of unvoiced consonants immediately precedes a vowel, THEN it will not itself be preceded by one or more voiced consonants.
The exceptions were found to be in almost all cases of nasal + homorganic unvoiced stop followed by a vowel, e.g. Chatino, Pame (both Oto-Manguean), Chrau (Mon-Khmer, Austroasiatic). The other instances of the interruption of voicing in an initial sequence are found in :Khasi (both Mon-Khmer, Austroasiatic), e.g. bt, dp; Bilaan (W. Malayo-Polynesian, Austronesian), e.g. bt, bs; Czech (Slavic, Indo-European), e.g. js. (Greenberg 1965: 20, 1978e: 260)
