Which scale do decibels use?

• A. Linear
• B. Ratio
• C. Arithmetic
• D. Logarithmic

Answer: (D)

The decibel scale is logarithmic. It expresses a ratio to a reference quantity using a log function, which is why loudness measurements are taken as 20 log10(p/p0) for sound pressure (or 10 log10(I/I0) for intensity). This log form matches how we perceive changes: large increases in actual quantity show up as modest steps on the scale, keeping numbers manageable across the immense range of sounds we experience.

A concrete implication is that equal steps in decibels correspond to multiplicative changes in the physical quantity. For example, a 10 dB increase means the intensity is about ten times greater, and a doubling of sound pressure corresponds to about a 6 dB increase. This is why the decibel scale is so well suited for acoustics: it compresses a huge range into a usable, perceptually meaningful scale.