The Lagrange Interpolation method uses a polynomial of order (n-1) where "n" is the number of data points used for interpolation. The "dsp.VariableFractionalDelay" object has a property "FilterLength" which allows the user to specify the number of points that are used in the Lagrange interpolation. Thus if the "FilterLength" is 2 the interpolation is linear, if the "FilterLength" is 3 the interpolation is quadratic, and so on.
For background on Lagrange interpolation see the following link:
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