The HTK Book Steve Young Gunnar Evermann Dan Kershaw ...

3.2 Creating Monophone HMMs 32macros~o 39~v "varFloor1" 390.0012 0.0003 ...hmmdefs~h "aa" ...~h "eh" ...... etcFig. 3.7Form of Master Macro FilesThe flat start monophones stored in the directory hmm0 are re-estimated using the embeddedre-estimation tool HERest invoked as followsHERest -C config -I phones0.mlf -t 250.0 150.0 1000.0 \-S train.scp -H hmm0/macros -H hmm0/hmmdefs -M hmm1 monophones0The effect of this is to load all the models in hmm0 which are listed in the model list monophones0(monophones1 less the short pause (sp) model). These are then re-estimated them using the datalisted in train.scp and the new model set is stored in the directory hmm1. Most of the files usedin this invocation of HERest have already been described. The exception is the file macros. Thisshould contain a so-called global options macro and the variance floor macro vFloors generatedearlier. The global options macro simply defines the HMM parameter kind and the vector size i.e.~o 39See Fig. 3.7. This can be combined with vFloors into a text file called macros.Prototype HMMDefinition(p r o t o )HCOMPVTraining Fileslisted in(t r a i n . s c p )HMM list( m o n o p h o n e s 0 )hmm0m a c r o sh m m d e f sHERESThmm1m a c r o sh m m d e f sPhone LevelTranscription(phones0.mlf)Fig. 3.8 Step 6The -t option sets the pruning thresholds to be used during training. Pruning limits the range ofstate alignments that the forward-backward algorithm includes in its summation and it can reducethe amount of computation required by an order of magnitude. For most training files, a very tightpruning threshold can be set, however, some training files will provide poorer acoustic matching