Determining slope of line relative to a maximum

Question

In the following scientific report (Seismic Q estimation), a mathematical procedure of linear curve-fitting is described in words. The authors state:

The stratigraphic effects are minimized by identifying the local dominant, or peak, spectral component and measuring the slope relative to that maximum over at least an octave above that component.

What is meant by measuring a slope relative to a maximum? In signal processing and music, an octave is either half or double the frequency.

Given that the frequency is plotted on the x-axis of the plot (abscissa), and the peak spectral component power is plotted on the y-axis (ordinate), the first step is to find the maximum ordinate value (as the peak spectral component). But how is the slope of the line $y= mx +b$ determined relative to the maximum?

Answer 1

Perhaps this is the most plausible description of the curve-fitting procedure.

1. Find the maximum ordinate value as $y_c$ at abscissa $x_c$. This is the first point of the vector of points over which to fit the line.
2. All other points that are $x_c\leq x \leq 2x_c$ are used to fit the linear equation of the line.