An example of symmetric comparison
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:
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.
Note 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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