Now, let us take a look at signal intensity. dB (decibel). When representing the magnitude of a signal or comparing other values in the communication system, very high range of values are used. bel is used to effectively represent the high range of values or to efficiently calculate comparisons as common logarithms. dB is used by multiplying 1/10 to bel, and used as a unit to measure the degree of weakness of a signal by comparing the initial signal and the transmitted signal. It is used as a unit to represent wave propagation. dB unit is not for absolute magnitude but relative magnitude between two signals. dB unit represents relative magnitude of the range of hearing at the reference of 0 dB. Please click the “next” button. The reason why common logarithms are used is to reflect the fact that auditory sense is proportional not to the magnitude of a sound itself but to its algebra (A sound 10,000 times in magnitude is heard by human beings as 40 times in magnitude). When a signal is reduced due to attenuation in the channel, its dB value is represented as a negative value. (For power, 3dB represents 2 times power value, -3dB 1/2 times power value. For voltage, 6dB represents 2 times voltage value, -6dB 1/2 times voltage value.)