FFT Analyzer Basic FAQ

In a power spectrum, a single line value (i.e., frequency band) represents the mean square, so its linear spectrum is the RMS value. However, since the analysis width (frequency resolution) of FFT analysis is usually small, its output can be approximated as a sine wave (or cosine wave). Therefore, the amplitude value (peak value, single amplitude value) at that frequency can be approximately calculated as √2 times the RMS value. This approximate peak value is sometimes called the equivalent peak value. Similarly, the PP value (peak-to-peak value, both amplitude values) can be obtained by multiplying the RMS value by √2.

For example, input signalTherefore, the effective value is A / √2, the amplitude value (peak value) is A, and the PP value is 2A.

	Power spectrum (FFT analyzer basic terminology glossary)