Fig. 1.

Concept of spectral bandwidth changes. Generally, spectral changes may differ with respect to the peak frequency of the responses (A). However, even if responses have the same peak frequency, they may differ with respect to their spectral bandwidth (blue and red curves in B). Gray lines indicate the full width at half maximum (FWHM): the width at which the amplitude decays to half its maximum value. (C) Power spectrum of a harmonic oscillator for different values of the damping, normalized to the peak value for damping constant ρ = 0.3. The FWHM is indicated for the curve of ρ = 0.3. (D) Inverse Q factor (black) as a function of the damping constant ρ. Peak value of the power spectrum as a function of the damping (gray). The dashed vertical line indicates the limit for which a FWHM can be defined. Beyond this line, the power does not decay below half the peak value at small frequencies. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)