I'm trying to find out what function is behind the set of data. On the plot there are two sets: `win2fs` and `win2fs-dec`. The first one is quite easy, because it is simply a sine/cosine function (for reference I've plotted it over the data set). But the second one is tricky for me... Does anyone know what might be the function for `win2fs-dec` (green x)? Maybe it's some kind of composition of trigonometrical functions...

The first one is a window function for MDCT and the second one is also a window function but for IMDCT (inverse of MDCT).

> https://en.wikipedia.org/wiki/Modified_discrete_cosine_transform