ABSTRACT
This chapter discusses the concepts underlying frequency analysis in detail and the analysis of signals using much narrower frequency bands than 1/3-octave. Spectral analysis is commonly carried out in standardised octave, 1/3-octave, 1/12-octave and 1/24-octave bands, and both analogue and digital filters are available for this purpose. Such filters are referred to as constant percentage bandwidth filters meaning that the filter bandwidth is a constant percentage of the band centre frequency. The auto power spectrum is the most common form of spectral representation used in acoustics and vibration. Sometimes the results of a spectral analysis are presented in terms of linear rather than the squared values of an auto power spectrum. Each frequency component in the linear spectrum is calculated by taking the square root of each frequency component in the auto power spectrum.
