Long description

This figure consists of two graphs, one above the other. They have the same horizontal axis, showing normalised frequency on a logarithmic scale from 0.01 to 100.

The upper graph is gain G against normalised frequency, where the vertical axis for gain is on a logarithmic scale from 0.01 to 1. The graph line is the same shape as the one shown in Figure 9. It starts at a gain of 1 for a normalised frequency of 0.01 and remains at this value up to a normalised frequency of just over 0.1. The graph line then begins to curve gently downwards, until it becomes a diagonally descending straight line with a gain of 0.2 at a normalised frequency of 5 and a gain of 0.02 at a normalised frequency of 50.

The lower graph is phase difference against normalised frequency, where the vertical axis for phase difference is on a linear scale from minus 90 degrees to zero. The graph line starts at a phase difference of zero for a normalised frequency of 0.01, then curves down at first gently and then more steeply until it becomes a diagonally descending straight line that reaches a phase difference of minus 45 degrees at a normalised frequency of 1. After this, the graph line continues to curve down at first steeply and then more gently, until it flattens out again at a phase difference of minus 90 degrees for a normalised frequency of 100. The overall shape of the graph line is a flattened, backwards S with rotational symmetry around the central point (the steepest part of the curve) at normalised frequency 1, phase difference minus 45 degrees.