13.13.2 Use

HREST is invoked via the command line

   HRest [options] hmm trainFiles ...

This causes the parameters of the given hmm to be re-estimated repeatedly using the data in trainFiles until either a maximum iteration limit is reached or the re-estimation converges. The HMM definition can be contained within one or more macro files loaded via the standard -H option. Otherwise, the definition will be read from a file called hmm. The list of train files can be stored in a script file if required.

The detailed operation of HREST is controlled by the following command line options

-c f
Set the threshold for tied-mixture observation pruning to f. When all mixtures of all models are tied to create a full tied-mixture system, the calculation of output probabilities is treated as a special case. Only those mixture component probabilities which fall within f of the maximum mixture component probability are used in calculating the state output probabilities (default 10.0).

-e f
This sets the convergence factor to the real value f. The convergence factor is the relative change between successive values of (default value 0.0001).

-i N
This sets the maximum number of re-estimation cycles to N (default value 20).

-l s
The string s must be the name of a segment label. When this option is used, HREST searches through all of the training files and cuts out all segments with the given label. When this option is not used, HREST assumes that each training file is a single token.

-m N
Sets the minimum number of training examples to be N. If fewer than N examples are supplied then an error is reported (default value 3).

-t
Normally, training sequences are rejected if they have fewer frames than the number of emitting states in the HMM. Setting this switch disables this reject mechanism.

-u flags
By default, HREST updates all of the HMM parameters, that is, means, variances, mixture weights and transition probabilities. This option causes just the parameters indicated by the flags argument to be updated, this argument is a string containing one or more of the letters m (mean), v (variance), t (transition) and w (mixture weight). The presence of a letter enables the updating of the corresponding parameter set.

-v f
This sets the minimum variance (i.e. diagonal element of the covariance matrix) to the real value f. This is ignored if an explicit variance floor macro is defined. The default value is 0.0.

-w f
Any mixture weight or discrete observation probability which falls below the global constant MINMIX is treated as being zero. When this parameter is set, all mixture weights are floored to f * MINMIX.

-B
Output HMM definition files in binary format.
-F fmt
Set the source data format to fmt.
-G fmt
Set the label file format to fmt.
-H mmf
Load HMM macro model file mmf. This option may be repeated to load multiple MMFs.
-I mlf
This loads the master label file mlf. This option may be repeated to load several MLFs.
-L dir
Search directory dir for label files (default is to search current directory).
-M dir
Store output HMM macro model files in the directory dir. If this option is not given, the new HMM definition will overwrite the existing one.
-X ext
Set label file extension to ext (default is lab).

HREST also supports the standard options -A, -C, -D, -S, -T, and -V as described in section 4.4.