neper

3.04  neper. Logarithmic unit for the amplitude ratio of two sinusoidal acoustic variables of the same kind, or for the ratio of a sinusoidal amplitude to a reference value of the same kind, when the logarithm is on the Napierian (natural) base e ≈ 2.7183.

Annotation 1          A logarithmic amplitude ratio of one neper corresponds to a difference between acoustic variables in decibels of 10log₁₀(e²), or approximately 8.686 decibels.

Annotation 2          If two sinusoidally varying acoustic variables have amplitudes q₁ and q₂ the quantities are said to differ in amplitude by ln(q₁/q₂) nepers.