Appendix C

Acoustic Spectra

Spectra representing sound pressure histories are usually presented in a special way, expressing the power in decibels (dB) in octave-based frequency bands, rather than as PSD plots. This method of presentation is largely due to two factors: (1) it was originally designed for studies involving human hearing, which has a naturally logarithmic response, and (2) it was based on the use of analog filter methods, which are more conveniently set up using bands consisting of a fixed fraction of an octave, rather than of a fixed number of hertz.

This method of presentation, although designed for audio work, using analog methods, has survived into the digital age, and is still widely used in purely structural applications. ...

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