Weights - Amazon Lex

Weights

You can add the weight attribute to an element. Weight is a positive floating point value that represents the degree to which the phrase in the item is boosted during speech recognition. For more information, see Weights in the Speech recognition grammar specification version 1 W3C recommendation.

Weights must be greater than 0 and less than or equal to 10, and can have only one decimal place. If the weight is greater than 0 and less than 1, the phrase is negatively boosted. If the weight is greater than 1 and less than or equal to 10, the phrase is positively boosted. A weight of 1 is equivalent to giving no weight at all, and there is no boosting for the phrase.

Assigning appropriate weights to items for improving speech recognition performance is a difficult task. Here are some tips you can follow for assigning weights:

  • Start with a grammar without item weights assigned.

  • Determine which patterns in the speech are frequently misidentified.

  • Apply different values for weights until you notice an improvement in the speech recognition performance, and there are no regressions.

Example 1

For example, if you have a grammar for airports, and you observe that New York is frequently misidentified as Newark, you can positively boost New York by assigning it a weight of 5.

<rule> id="airport">
    <one-of>
        <item>
            Boston
            <tag>out="Boston"</tag>
        </item>
        <item weight="5">
            New York
            <tag>out="New York"</tag>
        </item>
        <item>
            Newark
            <tag>out="Newark"</tag>
        </item>
    </one-of>
</rule>

Example 2

For example, you have a grammar for the airline reservation code starting with an English alphabet followed by three digits. The reservation code most likely starts with B or D, but you observe that B is frequently misidentified as P, and D as T. You can positively boost B and D.

<rule> id="alphabet">
    <one-of>
        <item>A<tag>out.letters+='A';</tag></item>
        <item weight="3.5">B<tag>out.letters+='B';</tag></item>
        <item>C<tag>out.letters+='C';</tag></item>
        <item weight="2.9">D<tag>out.letters+='D';</tag></item>
        <item>E<tag>out.letters+='E';</tag></item>
        <item>F<tag>out.letters+='F';</tag></item>
        <item>G<tag>out.letters+='G';</tag></item>
        <item>H<tag>out.letters+='H';</tag></item>
        <item>I<tag>out.letters+='I';</tag></item>
        <item>J<tag>out.letters+='J';</tag></item>
        <item>K<tag>out.letters+='K';</tag></item>
        <item>L<tag>out.letters+='L';</tag></item>
        <item>M<tag>out.letters+='M';</tag></item>
        <item>N<tag>out.letters+='N';</tag></item>
        <item>O<tag>out.letters+='O';</tag></item>
        <item>P<tag>out.letters+='P';</tag></item>
        <item>Q<tag>out.letters+='Q';</tag></item>
        <item>R<tag>out.letters+='R';</tag></item>
        <item>S<tag>out.letters+='S';</tag></item>
        <item>T<tag>out.letters+='T';</tag></item>
        <item>U<tag>out.letters+='U';</tag></item>
        <item>V<tag>out.letters+='V';</tag></item>
        <item>W<tag>out.letters+='W';</tag></item>
        <item>X<tag>out.letters+='X';</tag></item>
        <item>Y<tag>out.letters+='Y';</tag></item>
        <item>Z<tag>out.letters+='Z';</tag></item>
    </one-of>
</rule>