What is a Decibel?

You might have heard the term decibel, but what is it? The definition is based on the measurement of power in the telephony of the early 20th century in the Bell System in the United States.

One decibel is one tenth (deci-) of one bel, named after Alexander Graham Bell, but let us guide you through this unit of measurement.

  • The decibel is a unit of measurement used to express the ratio of one value of a physical property to another on a logarithmic scale.
  • Did you know the decibel originates from methods used to quantify signal loss in telegraph and telephone circuits?
  • Decibels can be used to express a change in value or an absolute value, expressing the ratio of a value to a reference value.
  • If it expresses the ratio, the decibel should be appended with a suffix that indicates the reference value or some other property. For example, if the reference value is 1 volt, then the suffix is “V” (e.g, “20 dBV”), and if the reference value is one milliwatt, then the suffix is “m” (e.g., “20 dBm”).
  • Depending on the nature of the quantities: field, power and root-power there are two different scales used when expressing a ratio in decibels. When expressing power quantities the number of decibels in ten times the logarithm to base 10. If we talk about field quantities the change in power by a factor of 10 corresponds to a 10 dB change in level.
  • In April 2003, the International Committee for Weights and Measures (CIPM) considered a recommendation for the inclusion of the decibel in the International System of Units (SI), but decided against the proposal.[11] However, the decibel is recognized by other international bodies such as the International Electrotechnical Commission (IEC) and International Organization for Standardization (ISO).
  • Decibels are not only used for acoustics, but also for perception, electronics, optics and video and digital imaging.

In short, decibels are used to express levels of sound meaningfully in numbers so that they are more manageable, and that is why we use a logarithmic scale, rather than a linear one. Zero decibels is the quietest sound audible to a healthy human ear. From there, every increase of 3dB represents a doubling of sound intensity or acoustic power.