While searching the forum I found the "defreq" plugin.
Now I try to use it. But I can't find good parameters. The sample on the website (
http://www.avisynth.org/fizick/defreq/defreq.html) is quite unlike my frequency spectrum. I do not have clear hot spots
And it's alternating frame by frame (see frame 9750 vs. 9751, middle region).
Images and avisynth script see link in 1st post.
Maybe someone can help?