Linked Questions

8
votes
1answer
10k views

Symmetry of real and imaginary parts in FFT [duplicate]

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4
votes
1answer
4k views

Why can the FFT always be mirrored in the middle of the x axis? [duplicate]

Plotting the FFT of a signal with Matlab e.g. by the code: y_fft = abs(fft(y)); f = fs*(0:length(y)-1)/length(y); plot(f,y_fft); where ...
83
votes
9answers
70k views

What is the physical significance of negative frequencies?

This has been one of the holes in my cheddar cheese block of understanding DSP, so what is the physical interpretation of having a negative frequency? If you have a physical tone at some frequency ...
14
votes
5answers
9k views

FFT of sine wave not coming as expected i.e single point

The cyan plot is a spectrum of 50 Hz, and the magenta one is a 50.1 Hz sine wave (having amplitude 0.7). Both are sampled at 1024 samples/s. I performed a 1024 point FFT to get this spectrum. Why is ...
5
votes
2answers
26k views

Amplitude of the Signal in Frequency Domain different from Time Domain

How does the Amplitude of the Signal is changed when taking the FFT of a Signal, Have a look, The amplitude had changed from 2 to 30, and Here is my code for generating the above output, ...
1
vote
1answer
2k views

FFT of a pure sine wave is not a single peak

For fun, I computed the FFT of a pure sine wave. I chose chose the sample length to be an even multiple of the signal period, so that I don't see windowing-effects. Here is the Matlab code that I used:...
1
vote
2answers
2k views

FFT of Square Wave and Sin Wave

When we have FFT of Square wave of a pure real signal with high frequency(close to f(max), less than half of sampling frequency) we see only 2 symmetric high peaks but when we decrease the frequency ...
3
votes
1answer
797 views

2D Fourier transform of Sobel kernel

Can someone explain me the highlighted text parts regarding this image ? Here is a pseudo-code of how it was created: ...
0
votes
2answers
599 views

Discrete Fourier transform of even function

I have a cosine function - Hence it is even. Considering only the real parts of the DFT, on performing DFT, I am getting something like this. Could anybody tell me where I am going wrong: DFT: ...
2
votes
1answer
355 views

General question about DFT

I am learning Fourier analysis and without any teacher, just trying to read books on my own. I think I have made some decent progress but they are a couple of points which are still very unclear to me ...
0
votes
2answers
270 views

How Discrete sequence could have more than one Frequency

I'm trying to understand Fast Fourier Transform in Detail to find out what exactly the frequencies when dealing with discrete sequence, Here is what I've done, First I've taken a Sinusoidal wave ...
1
vote
1answer
61 views

How to get some law parameters from its FFT figure?

Given an hidden law $$I(t)=\frac{1}{2}[A+B.cos(2\pi\nu_0t+\phi_0)]$$ I observe its signal with 256 samples and compute its FFT over this interval, and represent the FFT result from 0 to 1 (normalised ...