Decade (log scale)
One decade is a factor of 10 difference between two numbers (an order of magnitude difference) measured on a logarithmic scale. Along with the octave, it is a logarithmic unit used to describe frequency bands or frequency ratios. It is especially useful when referring to frequencies and when describing frequency response of electronic systems, such as audio amplifiers and filters.
The factor-of-ten in a decade can be in either direction: so one decade up from 100 Hz is 1000 Hz, and one decade down is 10 Hz. The factor-of-ten is what is important, not the unit used, so 3.14 rad/s is one decade down from 31.4 rad/s.
To determine the number of decades between two frequencies ( & ), use the logarithm of the ratio of the two values:
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