text: Its a mathematical function which converts the time domain data stream into the frequency domain (spectrum).\n\nOnce the spectral peaks have been identified, fixes and mods become pretty obvious. In addition, one can create a stored  baseline, and if a different spectral content is obsered, you know something has changed, and the frequencys of interest, can help you pin point the problem. An FFT analysis can predict early bearing failure, as well as hardnening of the mouting surfaces.