Surface filters are used to increase or decrease the amplitude of selected spectral components.
Filters must be first created, then their value can be defined.
The resulting filter will be automatically converted into a basic grey surface filter. It will be first superimposed on the blue time/frequency region, which will disappear when unselected.
Note that filters are continuous surfaces, contrary to time frequency regions.
A standard " Surface Filter" block will be displayed in the processing sequencer.