Howtosignalprocessing
- Why does FFT have negative frequencies?
- What do negative values in FFT mean?
- Why are there negative frequencies?
- Can FFT be negative?
Why does FFT have negative frequencies?
The reason is that the Fourier transform is symmetric about the y-axis, because the Fourier transform is mathematically defined on the interval (-Inf,Inf). The actual Fourier transform therefore has negative frequencies.
What do negative values 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.
Why are there 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.
Can FFT be negative?
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.
