Suggested improvements to the spectrum plot

The spectrum plot would be more useful if:

  1. the amplitude could be normalised such that the max value is 0 dB
  2. it would be useful to plot below - 90 dB, so the lower end of the graph ought to be configurable
  3. it would also be useful to be able to zoom the frequency axis
    I do not know the code, so I am not sure how much work it would be to implement these features though.

Voxengo SPAN plugin (free) has those features