In Level building, unlike in Viterbi search, HMM for each speech unit is considered separately [, ]. The search is performed at various levels for each HMM using the Viterbi algorithm, where a level corresponds to the position of the speech unit within the possible sentence. After searching at each level, we find the maximum Viterbi score over all speech unit models for every time frame t. The search in next level starts with the winning score of the previous level at previous time frame. After having completed searches in levels, the sequence of winning speech unit model at levels in that order represents the possible sentence which is speech units long. In order to find the optimum sentence a maximization is done over within a reasonable range.