A bel (in honor of Alexander Graham Bell) is a measure of the ratio between two quantities, usually the ratio between the input and output powers of an electrical system, calculated in the logarithmic scale, where one decibel (dB) is equal to ten bels. In digital filter design, decibels are used to emphasize the description of attenuations in the amplitude of a signal at different frequencies, where decibels are calculated as 20 times the base-10 logarithm of the ratio between two amplitudes.