Calculating similarity between two signal plots I have two plots, each having frequency as x-axis and Gain as y-axis. By taking one data set as a reference I have to calculate similarity between them. 

The graphs have same values on the x-axis and have same range on the x axis

Can 2D Correlation or Co-variance can do a decent job ? or
should I opt for Fréchet distance or DWT as I have read in some other posts ?

The first plot is the reference plot.

Here are the plots:



Please help!
Why not just use something like the relative "error" between the two?

For example, if your frequency magnitude responses are $G_1$ and $G_2$, then calculate:

$$
ERR = \sum \left | G_1(n) - G_2(n) \right|^2
$$

and then normalize with respect to the reference, $G_1$:

$$
NORMALIZED = \sum \left | G_1(n) - G_2(n) \right|^2 /  \sum \left | G_1(n) \right|^2
$$

Correlation is also a way to go, but it might show some cases where the same shape happens, but at very different frequencies... which might not be what you want.