This corresponds roughly to our greater sensitivity to lower frequencies.

Linear Frequency Scale: When this box is unchecked, the horizontal frequency scale is logarithmic, giving more detail at the lower frequencies.The green curve usually follows the blue curve closely, but will be forced to a smoother path if there are sudden changes in amplitude over a small frequency range. The green curve is the one that Audacity actually uses to perform the effect, taking into account the limitations of the equalization algorithm. To remove a control point, drag it outside the graph.

Doing either creates a control point at that position, then creating further control points draws the curve. When in ' Draw Curves' mode, the blue curve is drawn by either clicking in the graph at any position, or clicking on the blue curve and dragging it to a position. The white circles are called 'control points'. Equalization Curves and Control Points: If you look closely at the curve in the image above, you'll see it's composed of a blue curve joining together a number of white circles, and a green curve which follows the general shape of the blue curve.

Audacity filter curve