I have been recently working with the FFT and realized that each frequency within a bin corresponds to a phase. I understand why a phase that corresponds to each frequency is needed because it allows one to construct the original signal from those sinusoidal waves.

Currently I am trying see if a specific signal corresponds to a specific sound.

My Question

When characterizing a signal with FFT, is good practice to just use the frequency of the bins and ignore the corresponding phases?


2 Answers 2


It depends,

sometimes phase matters and sometimes it doesn’t.

There is a paper by Oppenheim.

Oppenheim, Alan V., and Jae S. Lim. "The importance of phase in signals." Proceedings of the IEEE 69.5 (1981): 529-541.

where an image is reconstructed with just phase and with just magnitude. The phase only image is nearly the same while amplitude alone is a mess.

For something like a stationary random noise, the signal model explicitly notes that the phase is random and is ignored.

There are probably a lot of cases where people ignore phase because it’s easier. Phase unwrapping can be difficult. Interpretation can be difficult.

For cross correlation phase is very important.

It's never good practice to do things blindly.


In short: yes.

When talking audio signals and their spectra, one ususally is referring to their magnitude spectra, and then also usually on a double log scale, because this is how human hearing works.

The phase, in contrast, is mostly ignored, as the human hearing system cannot perceive it per se. Phase diagrams do come handy, when talking loudspeaker design for example, as phase differences can be perceived, namely as narrow notches in the frequency response of a two way loudspeaker box close to its crossover frequency.

But in general, when talking about signals, phase will be ignored.

  • $\begingroup$ I disagree with your last sentence, but other than that I think your answer is good. $\endgroup$
    – Ben
    Commented Jul 17, 2019 at 16:55

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