Long description

This figure is a graph of gain against normalised frequency. The horizontal axis shows normalised frequency on a logarithmic scale from 0.001 to 1000. Two vertical axes are used for the gain, one showing power gain in decibels from minus 60 to 10, and the other showing the equivalent voltage gain.

The graph line starts at a power gain of 0 decibels (voltage gain of 1) for a normalised frequency of 0.001, and remains at this value up to a normalised frequency of around 0.3.

The graph line then begins to curve gently downwards, reaching a power gain of minus 3 decibels (voltage gain of 0.707) at a normalised frequency of 1. This frequency is the cut-off frequency.

Above the cut-off frequency, the graph line continues to curve downwards until it becomes a diagonally descending straight line. This line has a power gain of minus 20 decibels (voltage gain of 0.1) at a normalised frequency of 10 and a power gain of minus 40 decibels (voltage gain of 0.01) at a normalised frequency of 100, meaning that the slope of the line is minus 20 decibels per decade.

Frequencies below the cut-off frequency of 1 are in the passband, while frequencies above the cut-off frequency are in the stop band.