The phonological system of Russian is inherited from Common Slavonic, but underwent considerable modification in the early historical period, before being largely settled by about 1400.
The language possesses five vowels, which are written with different letters depending on whether or not the preceding consonant is palatalized. The consonants typically come in plain vs. palatalized pairs, which are traditionally called hard and soft. (The hard consonants are often velarized, especially before back vowels, although in some dialects the velarization is limited to hard /l/). The standard language, based on the Moscow dialect, possesses heavy stress and moderate variation in pitch. Stressed vowels are somewhat lengthened, while unstressed vowels tend to be reduced to near-close vowels or an unclear schwa. (See also: vowel reduction in Russian.)
The Russian syllable structure can be quite complex with both initial and final consonant clusters of up to 4 consecutive sounds. Using a formula with V standing for the nucleus (vowel) and C for each consonant the structure can be described as follows:
Clusters of four consonants are not very common, however, especially within a morpheme. Free Quote