# Distortion (Sound and Vibration)

## Sound and Vibration Measurement Help

Edition Date: March 2018
Part Number: 372416L-01
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Distortion is the addition of signal components that are not part of the original signal. You can find these additional components in harmonics and intermodulations of the input frequencies. Distortion is generally an unwanted response because of non-linearities in the device under test.

Distortion measurements use the following equations:

$\sum {P}_{\mathrm{Harmonics}}=\sqrt{\left({H}_{2}{\right)}^{2}+\left({H}_{3}{\right)}^{2}+...+\left({H}_{K}{\right)}^{2}}$
$\sum {P}_{\mathrm{Harmonics}}+\sum {P}_{\mathrm{Noise}}=\sqrt{\left({H}_{2}{\right)}^{2}+\left({H}_{3}{\right)}^{2}+...+\left({H}_{K}{\right)}^{2}+\left(N{\right)}^{2}}$
$\sum {P}_{\mathrm{Noise}}=\sqrt{\left(F{\right)}^{2}+\left({H}_{2}{\right)}^{2}+...+\left({H}_{K}{\right)}^{2}+\left(N{\right)}^{2}}$

where specific signal components are identified as

F is the fundamental tone root mean square (RMS) level

K is the maximum harmonic in the measurement bandwidth

H i is the ith harmonic RMS level, where i is an integer <2..K>

N is the noise RMS level