Linked Questions

10 votes
1 answer
14k views

Symmetry of real and imaginary parts in FFT [duplicate]

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gpuguy's user avatar
  • 1,370
4 votes
1 answer
6k 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 ...
Morten's user avatar
  • 333
0 votes
0 answers
34 views

Why are these excess frequency components in my FFT spectrum? [duplicate]

I am experimenting with digital signal processing and I took the FFT of a sinusoid in Matlab. I got the frequency components that I expected to be present but there are two excess spikes that mirror ...
Michael's user avatar
118 votes
12 answers
102k 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 ...
Spacey's user avatar
  • 9,817
17 votes
5 answers
14k 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 ...
gpuguy's user avatar
  • 1,370
8 votes
2 answers
32k 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, ...
Sufiyan Ghori's user avatar
3 votes
1 answer
3k 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: ...
james's user avatar
  • 113
0 votes
1 answer
2k views

Conjugate symmetry of the DFT of real-valued sequences

I have read about Fourier transformation that real signals are "mirrored" in the real and negative halves of the Fourier transform because of the nature of the Fourier transform. For ...
Gze's user avatar
  • 640
2 votes
1 answer
3k 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:...
Martin J.H.'s user avatar
1 vote
2 answers
4k 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 ...
Anarkie's user avatar
  • 137
0 votes
2 answers
2k 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: ...
user11438's user avatar
0 votes
1 answer
991 views

Complex signal low pass filter

I'm trying to implement a low pass filter in python for a complex signal but the output doesn't look right. I've created a simple example below where I've mixed a 15Hz complex sine wave and a 30Hz ...
user1759872's user avatar
1 vote
1 answer
684 views

Why does the frequency window affect the inverse fourier transform oscillation frequency?

I have an oscillating pulse in the frequency domain that I would like to inverse Fourier transform. My signal looks like: Which was coded in MATLAB using the following code: ...
dljs's user avatar
  • 13
0 votes
2 answers
286 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 ...
Sufiyan Ghori's user avatar
2 votes
1 answer
427 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 ...
mast4as's user avatar
  • 21

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