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The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a power ratio of 10 1/10 (approximately 1.26) or root-power ratio of 10 1/20 (approximately 1.12). [1] [2]
In many cases, attenuation is an exponential function of the path length through the medium. In optics and in chemical spectroscopy , this is known as the Beer–Lambert law . In engineering, attenuation is usually measured in units of decibels per unit length of medium (dB/cm, dB/km, etc.) and is represented by the attenuation coefficient of ...
Most commonly, the quantity measures the exponential decay of intensity, that is, the value of downward e-folding distance of the original intensity as the energy of the intensity passes through a unit (e.g. one meter) thickness of material, so that an attenuation coefficient of 1 m −1 means that after passing through 1 metre, the radiation ...
[a] A more precise model known as the Inflected Exponential function, [3] indicates that loudness increases with a higher exponent at low and high levels and with a lower exponent at moderate levels. [4] The sensitivity of the human ear changes as a function of frequency, as shown in the equal-loudness graph. Each line on this graph shows the ...
Semi-log plot of the Internet host count over time shown on a logarithmic scale. A logarithmic scale (or log scale) is a method used to display numerical data that spans a broad range of values, especially when there are significant differences between the magnitudes of the numbers involved.
A gain greater than one (greater than zero dB), that is, amplification, is the defining property of an active device or circuit, while a passive circuit will have a gain of less than one. [ 4 ] The term gain alone is ambiguous, and can refer to the ratio of output to input voltage ( voltage gain ), current ( current gain ) or electric power ...
High-powered transmissions, such as those used in broadcasting, are expressed in dB-millivolts per metre (dBmV/m). For very low-power systems, such as mobile phones, signal strength is usually expressed in dB-microvolts per metre (dBμV/m) or in decibels above a reference level of one milliwatt .
While describing sound in terms of sound pressure, a logarithmic conversion is usually applied and the sound pressure level is stated instead, in decibels (dB), with 0 dB SPL equal to 20 micropascals. A microphone is distinguishable by the voltage value produced when a known, constant root mean square sound pressure is applied. This is known as ...