How can I redraw a line in the diagram

[denzjos]

So I tried:
Make a copy layer
Make a path from the dB lines
Stroke the path with white
Copy the left side of the drawing to a new layer, flip it horizontal and drag it in place
Do the same with part of the upper side of the drawing and flip it vertical
Optimise the rest (two vertical lines in the center)
Make a new layer and stroke the path with red
   

  dB path.xcf (Size: 83.78 KB / Downloads: 90)