·Pure
 beam-pruning has long-tailed distribution of active HMMs/frame
 ·Absolute
 pruning to control worst-case performance:
 ·Max.
 active HMMs per frame
 ·Implemented
 approximately, using “histogram pruning” (avoids expensive sorting
 step)
 ·Max.
 unique words exiting per frame
 ·Max.
 LM histories saved in BP table per frame
 ·Word
 error rate unaffected
 ·Additional
 beam for lextree-internal, cross-HMM transitions
 ·Unigram
 “lookahead” scores used in lextree for yet more pruning