# Decibel FAQs:

Q: Is a decibel used to express the level of the other value relative to this reference?

A: Yes.

Q: Are decibels ten times the logarithm to base 10 of the ratio of two power quantities?

A: Yes, and or of the ratio of the squares of two field amplitude quantities.

Q: Are decibels awkward in inherently additive operations: "if two machines each individually produce a [sound pressure] level of"?

A: Yes, and say, 90 dB at a certain point, then when both are operating together we should expect the combined sound pressure level to increase to 93 dB, but certainly not to 180 dB!" "suppose that the noise from a machine is measured and found to be 87 dBA but when the machine is switched off the background noise alone is measured as 83 dBA.

Q: Is a decibel often used to express power or amplitude ratios?

A: Yes, and in preference to arithmetic ratios or percentages.

Q: Are decibels ten times the number of bels?

A: Yes, P and P0 must measure the same type of quantity, and have the same units before calculating the ratio.

Q: Is a decibel defined as a unit of measurement for quantities of type level or level difference?

A: Yes, and which are defined as the logarithm of the ratio of power- or field-type quantities.

Q: Was a decibel the proposed working unit?

A: Yes.

Q: Are decibels the traditional way of expressing gain or margin in such diverse disciplines as control theory?

A: Yes, and antenna and radio frequency transmission theory, and even assessment of nuclear hardness.

Q: Is a decibel based on the measurement of power in telephony of the early 20th century in the Bell System in the United States?

A: Yes.

Q: Is a decibel one tenth of one bel, named in honor of Alexander Graham Bell?

A: Yes, however, the bel is seldom used.

Q: Is a decibel recognized by other international bodies such as the International Electrotechnical Commission and International Organization for Standardization?

A: Yes, The IEC permits the use of the decibel with field quantities as well as power and this recommendation is followed by many national standards bodies, such as NIST, which justifies the use of the decibel for voltage ratios.

Q: Is a decibel accepted for use alongside SI units?

A: Yes, and the practice of attaching a suffix to the basic dB unit, forming compound units such as dBm, dBu, dBA, etc.

Q: Are decibels still the commonly used units to express ratios in a number of fields?

A: Yes, and even when the original meaning of the term is obscured.

Q: Is a decibel defined with respect to power?

A: Yes, and not amplitude, conversions of voltage ratios to decibels must square the amplitude, or use the factor of 20 instead of 10, as discussed above.

Q: Is a decibel commonly used in acoustics as a unit of sound pressure level?

A: Yes.