• decibel
  • A unit used to express relative difference on power, usually between acoustic or electric signals, equal to ten times the common logarithm of the ratio of the two level.
Abstract from DBPedia
    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 101/10 (approximately 1.26) or root-power ratio of 101⁄20 (approximately 1.12). The unit expresses a relative change or an absolute value. 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. For example, for the reference value of 1 volt, a common suffix is "" (e.g., "20 dBV"). Two principal types of scaling of the decibel are in common use. When expressing a power ratio, it is defined as ten times the logarithm in base 10. That is, a change in power by a factor of 10 corresponds to a 10 dB change in level. When expressing root-power quantities, a change in amplitude by a factor of 10 corresponds to a 20 dB change in level. 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. 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. The bel was named in honor of Alexander Graham Bell, but the bel is seldom used. Instead, the decibel is used for a wide variety of measurements in science and engineering, most prominently in acoustics, electronics, and control theory. In electronics, the gains of amplifiers, attenuation of signals, and signal-to-noise ratios are often expressed in decibels.

    デシベル (英語: decibel 記号: dB)は、ある物理量を基準となる量との比の常用対数によって表したものである。音の強さ、音圧レベル、電力比や電気機器の利得等を表すことが多い。 (一般化、抽象化して説明すると)「デシベル」というのは音圧、電力、利得など、物理量をレベル表現を用いて表すときに使用される単位である。(なおSIにおいてレベル表現として表される量には次元が与えられておらず、無次元量である。)電気工学や振動・音響工学などの分野で頻用される。