【请教】关于third octave spectra

一戒书生

今天阅读关于NVH的相关资料时，看到里面频繁出现third octave spectra，却不知道什么意思，上网查了一下，叫做3倍频谱，但是没找到更多的资料，请坛子里有相关资料的兄弟不吝赐教！！非常感谢！
原文资料内容之一：
In order to assess the vibration characteristics of engine components by means of the
third octave spectra of vibration velocity, an empirically based borderline of 100 dB can
be considered for rated power condition and for the frequency range above 400 Hz (the
peaks occurring below 400 Hz at frequencies of major engine orders may have higher
levels).