Russian words have one stressed syllable. The stress may fall on the first, second, third etc. syllable of a word. The  stressed syllable is longer and is articulated more tensely than the unstressed ones. In unstressed syllables the vowels undergo reduction and are shorter, while the vowels [à], [o] and [ý] change their timbre.

O when stressed -> [o]. O when unstressed -> [a]. In an unstressed position [o] is pronounced in the same way as [a] in an identical position.

Ìîäåëü -  Model

ÒÀ

ÒÀÒÀ

ÒÀÒÀ

 ÒÀ

  ÄÀ

 ÒÀÒÀ

  ÒÀÒÀ

 ÎÍÀ [àíà]