Negative values of the FFT

1. What does a negative value in FFT mean?
2. Can FFT have negative values?
3. What does negative Fourier transform mean?
4. Why is the Fourier transform negative?
5. What is the meaning of negative frequencies?
6. What do FFT values mean?

What does a negative value in FFT mean?

Negative values in the real component of the result of a complex FFT correspond to a negative correlation with a cosine waveform (same as a 180 degree phase shift). If you want to check the energy at each frequency, graph the magnitude (sqrt(rere+imim)) of each complex FFT result bin.

Can FFT have negative values?

FFT gave a result in complex coordinates. Absolute value of all data points should be taken . Power values are absolute values of complex numbers derived from FFT. They can not be negative unless they are contrasted to baseline or other conditions.

What does negative Fourier transform mean?

A negative real component just means the correlation against that particular cosine wave is negative, e.g. the input waveform seems to wiggle in the opposite direction of the corresponding cosine function, goes mostly low when the cosine goes high and vice versa. Same for the imaginary component and the sine function.

Why is the Fourier transform negative?

The negative sign in the forward Fourier Transform (FT) is just a convention, and sets the direction in which your signal is wrapped around the unit circle. Using a positive sign changes the sign of the imaginary part of the spectrum. However, you should always use the opposite sign in the inverse FT (IFT)!

What is the meaning of negative frequencies?

Negative frequency is an idea associated with complex exponentials. A single sine wave can be broken down into two complex exponentials ('spinning numbers'), one with a positive exponent and one with a negative exponent. That one with the negative exponent is where you get the concept of a negative frequency.

What do FFT values mean?

The "Fast Fourier Transform" (FFT) is an important measurement method in the science of audio and acoustics measurement. It converts a signal into individual spectral components and thereby provides frequency information about the signal.