In electronics, the gains of amplifiers, attenuation of signals, and signal-to-noise ratios are often expressed in decibels. Instead, the decibel is used for a wide variety of measurements in science and engineering, most prominently for sound power in acoustics, in electronics and control theory. The bel was named in honor of Alexander Graham Bell, but the bel is seldom used. A conversation is roughly 1 million times more intense than the threshold value. It is represented by the equation where is the threshold of hearing and is the intensity of the sound. The decibel (dB) system of sound intensity is a measure of how loud a sound is to ones ears. The definition of the decibel originated in the measurement of transmission loss and power in telephony of the early 20th century in the Bell System in the United States. Sound - The way sound is picked up by ones ears is of logarithmic nature. The decibel scales differ by a factor of two, so that the related power and root-power levels change by the same value in linear systems, where power is proportional to the square of amplitude. When expressing root-power quantities, a change in amplitude by a factor of 10 corresponds to a 20 dB change in level.
That is, a change in power by a factor of 10 corresponds to a 10 dB change in level. When expressing a power ratio, it is defined as ten times the logarithm in base 10. A decibel is a ratio of the observed amplitude, or intensity level to a reference, which is 0 dB. Two principal types of scaling of the decibel are in common use. For example, for the reference value of 1 volt, a common suffix is " V" (e.g., "20 dBV"). The top right graph uses a log-10 scale for just the X axis, and the bottom right graph uses a log-10 scale for both the X axis and the Y axis. In the latter case, the numeric value expresses the ratio of a value to a fixed reference value when used in this way, the unit symbol is often suffixed with letter codes that indicate the reference value. A base-10 log scale is used for the Y axis of the bottom left graph, and the Y axis ranges from 0.1 to 1,000. The unit expresses a relative change or an absolute value. The dB scale was invented by telephone engineers, and a deci Bell is 1/10 th of a Bell, which we define below.
Logarithmic unit expressing the ratio of physical quantities The decibel scale is useful in defining ratios of numbers, which may vary over many orders of magnitude (powers of 10).