<sect1 id='viterbi-manual'>
	<title><command>viterbi</command> <emphasis>Combine n-gram model and likelihoods to estimate posterior probabilities</emphasis></title>

    <toc depth='1'></toc>
    <para>
    </para>
    <sect2>
      <title>Synopsis</title>
      <para>
      </para>
        <!-- /amd/projects/festival/versions/v_mpiro/speech_tools_linux/bin/viterbi -sgml_synopsis -->
        <para>
<cmdsynopsis><command>viterbi</command>[observations file] -o [output file]<arg>-ngram <replaceable>string</replaceable></arg>
<arg>-given <replaceable>string</replaceable></arg>
<arg>-vocab <replaceable>string</replaceable></arg>
<arg>-ob_type <replaceable>string</replaceable></arg>
<arg>-lm_floor <replaceable>float</replaceable></arg>
<arg>-lm_scale <replaceable>float</replaceable></arg>
<arg>-ob_floor <replaceable>float</replaceable></arg>
<arg>-ob_scale <replaceable>float</replaceable></arg>
<arg>-prev_tag <replaceable>string</replaceable></arg>
<arg>-prev_prev_tag <replaceable>string</replaceable></arg>
<arg>-last_tag <replaceable>string</replaceable></arg>
<arg>-default_tags </arg>
<arg>-observes2 <replaceable>string</replaceable></arg>
<arg>-ob_floor2 <replaceable>float</replaceable></arg>
<arg>-ob_scale2 <replaceable>float</replaceable></arg>
<arg>-ob_prune <replaceable>float</replaceable></arg>
<arg>-n_prune <replaceable>int</replaceable></arg>
<arg>-prune <replaceable>float</replaceable></arg>
<arg>-trace </arg>
</cmdsynopsis>
        </para>
        <!-- DONE /amd/projects/festival/versions/v_mpiro/speech_tools_linux/bin/viterbi -sgml_synopsis -->
      <para>

viterbi is a simple time-synchronous Viterbi decoder. It finds the
most likely sequence of items drawn from a fixed vocabulary, given
frame-by-frame observation probabilites for each item in that
vocabulary, and a ngram grammar. Possible uses include:
<itemizedlist>
<listitem><para>Simple speech recogniser back end</para></listitem>
</itemizedlist>
viterbi can optionally use two sets of frame-by-frame observation
probabilites in a weighted-sum fashion. Also, the ngram language model
is not restricted to the conventional sliding window type in which the
previous n-1 items are the ngram context. Items in the ngram context
at each frame may be given. In this case, the user must provide a file
containing the ngram context: one (n-1) tuple per line. To include
items from the partial Viterbi path so far (i.e. found at recognition
time, not given) the special notation <-N> is used where N indicates
the distance back to the item required. For example <-1> would
indicate the item on the partial Viterbi path at the last frame. See
\Ref{Examples}.
<formalpara>
<para><title>Pruning</title></para>
<para>
Three types of pruning are available to reduce the size of the search
space and therefore speed up the search:
<itemizedlist>
<listitem><para>Observation pruning</para></listitem>
<listitem><para>Top-N pruning at each frame</para></listitem>
<listitem><para>Fixed width beam pruning</para></listitem>
</itemizedlist>
</para>
</formalpara>
      </para>
    </sect2>
    <sect2>
      <title>Options</title>
      <para>
      </para>
        <!-- /amd/projects/festival/versions/v_mpiro/speech_tools_linux/bin/viterbi -sgml_options -->
        <para>
<variablelist>
<varlistentry><term>-ngram</term>
<LISTITEM><PARA>
<replaceable>string</replaceable>

Grammar file, required 
</PARA></LISTITEM>
</varlistentry>

<varlistentry><term>-given</term>
<LISTITEM><PARA>
<replaceable>string</replaceable>

ngram left contexts, per frame 
</PARA></LISTITEM>
</varlistentry>

<varlistentry><term>-vocab</term>
<LISTITEM><PARA>
<replaceable>string</replaceable>

File with names of vocabulary, this 
must be same number as width of observations, required 
</PARA></LISTITEM>
</varlistentry>

<varlistentry><term>-ob_type</term>
<LISTITEM><PARA>
<replaceable>string</replaceable>

Observation type : likelihood .... and change doc"probs" or "logs" (default is "logs") 
Floor values and scaling (scaling is applied after floor value) 
</PARA></LISTITEM>
</varlistentry>

<varlistentry><term>-lm_floor</term>
<LISTITEM><PARA>
<replaceable>float</replaceable>

LM floor probability 
</PARA></LISTITEM>
</varlistentry>

<varlistentry><term>-lm_scale</term>
<LISTITEM><PARA>
<replaceable>float</replaceable>

LM scale factor factor (applied to log prob) 
</PARA></LISTITEM>
</varlistentry>

<varlistentry><term>-ob_floor</term>
<LISTITEM><PARA>
<replaceable>float</replaceable>

Observations floor probability 
</PARA></LISTITEM>
</varlistentry>

<varlistentry><term>-ob_scale</term>
<LISTITEM><PARA>
<replaceable>float</replaceable>

Observation scale factor (applied to prob or log prob, depending on -ob_type) 
</PARA></LISTITEM>
</varlistentry>

<varlistentry><term>-prev_tag</term>
<LISTITEM><PARA>
<replaceable>string</replaceable>

tag before sentence start 
</PARA></LISTITEM>
</varlistentry>

<varlistentry><term>-prev_prev_tag</term>
<LISTITEM><PARA>
<replaceable>string</replaceable>

all words before 'prev_tag' 
</PARA></LISTITEM>
</varlistentry>

<varlistentry><term>-last_tag</term>
<LISTITEM><PARA>
<replaceable>string</replaceable>

after sentence end 
</PARA></LISTITEM>
</varlistentry>

<varlistentry><term>-default_tags</term>
<LISTITEM><PARA>

use default tags of !ENTER,!EXIT and !EXIT 
respectively 
</PARA></LISTITEM>
</varlistentry>

<varlistentry><term>-observes2</term>
<LISTITEM><PARA>
<replaceable>string</replaceable>

second observations (overlays first, ob_type must be same) 
</PARA></LISTITEM>
</varlistentry>

<varlistentry><term>-ob_floor2</term>
<LISTITEM><PARA>
<replaceable>float</replaceable>

</PARA></LISTITEM>
</varlistentry>

<varlistentry><term>-ob_scale2</term>
<LISTITEM><PARA>
<replaceable>float</replaceable>

</PARA></LISTITEM>
</varlistentry>

<varlistentry><term>-ob_prune</term>
<LISTITEM><PARA>
<replaceable>float</replaceable>

observation pruning beam width (log) probability 
</PARA></LISTITEM>
</varlistentry>

<varlistentry><term>-n_prune</term>
<LISTITEM><PARA>
<replaceable>int</replaceable>

top-n pruning of observations 
</PARA></LISTITEM>
</varlistentry>

<varlistentry><term>-prune</term>
<LISTITEM><PARA>
<replaceable>float</replaceable>

pruning beam width (log) probability 
</PARA></LISTITEM>
</varlistentry>

<varlistentry><term>-trace</term>
<LISTITEM><PARA>

show details of search as it proceeds </PARA></LISTITEM>
</varlistentry>
</variablelist>
        </para>
        <!-- DONE /amd/projects/festival/versions/v_mpiro/speech_tools_linux/bin/viterbi -sgml_options -->
    </sect2>
    <sect2>
      <title>Examples</title>
      <para>
Example 'given' file (items f and g are in the vocabulary), the ngram
is a 4-gram.
<para>
<screen>
<-2> g g
<-1> g f
<-1> f g
<-2> g g
<-3> g g
<-1> g f
</screen>
</para>
      </para>
    </sect2>
  </sect1>