FFT Analyzer Basic FAQ

Phase refers to the positional information of a periodically fluctuating wave, for example, in an input signal.In a cosine wave (or sine wave) like this, (ωt + φ) is the angle (phase angle). Here, the phase φ at t = 0 is specifically called the initial phase, and this φ is usually referred to simply as the phase.

Phase display is based on the cosine waveform.Assuming φ = 0, a positive φ indicates a phase lead, and a negative φ indicates a phase lag. This phase component, expressed as a function of frequency, is called the phase spectrum, and it represents the phase angle in a 1-channel analysis with the data acquisition point as the reference. The unit of the phase angle is radians (rad), so the vertical axis of the phase spectrum is-π < φ ≤ π. However, in FFT analyzers, for ease of understanding, it is usually expressed in degrees, i.e., -180 deg < φ ≤ 180 deg.

 

Phase spectrum (FFT basic terminology glossary)