1. A machine-implemented method comprising: extracting portions from segment boundary regions of a plurality of speech segments, each segment boundary region based on a corresponding initial unit boundary; defining a vector space that represents the portions of the plurality of speech segments to derive feature vectors; for each of a plurality of potential unit boundaries within each segment boundary region, determining an average discontinuity based on distances between the feature vectors in the vector space; and for each segment, selecting a new unit boundary from the plurality of potential unit boundaries, wherein the new unit boundary is associated with a minimum average discontinuity.