Symmetric comparisons
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An example of symmetric comparison

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We will now use the same example presented above to demonstrate the effect of symmetric scoring, starting from an example that demonstrates the weakness of this approach. Keeping the setting of 8E, go to the ‘Similarity’ page and click ‘Symmetric’, click score:

graphic As you can see, the similarity is estimated from the beginning of the two sounds. Only sections are calculated, and the comparison is strictly on the 450 of the matrix, except that it has some (10ms) thickness. This thickness can be manipulated by moving the ‘min dur’ slider. 



graphicNote that reversing the order of Example 1 and Example 2 has only a minor effect on the similarity values (including % similarity).

To get the symmetric comparison to behave properly in this case, we need to manually segment the syllable in Example 2:
So, when should one use symmetric comparisons? These measurements are the best choice if we know in advance the sound units that should be compared and if we do not categorize one sound as a model for the other. For example, comparing two calls of the same type across different members of a colony calls for symmetric scoring. Also, once we have identified a cluster of syllables we might want to measure the similarity across sounds of this cluster, here too, a symmetric approach is most appropriate. SA+ provides a method for automatically identifying clusters across files and scoring their similarity (allowing batching of many thousands of comparisons, see batch operations for details).

  

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