The spectrum above plots the logarithm of the vibration level rather than the level itself.Logarithmic Amplitude Scaling
The spectrum above plots the logarithm of the vibration level rather than the level itself.
Since this spectrum is on a log amplitude scale, multiplication by any constant value simply translates the spectrum up on the screen without changing its shape or the relationship between the components.
Multiplication of the signal level translates into addition on a log scale. This means that if the amount of amplification of a vibration signal is changed, the shape of the spectrum is not affected. This fact greatly simplifies visual interpretation of log spectra taken at different amplification factors -- the curves are simply translated up or down on the graph. With a linear scaling, the shape of the spectrum changes drastically with different degrees of amplification.
The next spectrum is presented in decibels, a special type of log scaling that is very important in vibration analysis
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