Linked Questions

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 ...
119 votes
12 answers
103k 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 ...
2 votes
1 answer
429 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
1 answer
63 views

Sampling of sine wave :which one to choose? start with zeroth sample or 1st sample

sampling rate=200KHz signal freq =1KHz When I sample 1KHz signal I'll get 200 samples. Should I consider 0 to 199 samples? Or 1 to 200? I want only 1 cycle.
0 votes
1 answer
1k 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 ...
1 vote
0 answers
69 views

Asymmetry In The Mirroring Of An FFT Of A Sinusoidal Signal

I am trying to implement a Cooley-Tukey FFT algorithm in its iterative version. Specifically, I am implementing this Wikipedia pseudocode (please look at the section Data reordering, bit reversal, and ...
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 ...
1 vote
1 answer
695 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: ...
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: ...
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 ...
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: ...
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 ...
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:...
10 votes
1 answer
14k views

Symmetry of real and imaginary parts in FFT [duplicate]

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4 votes
1 answer
7k 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 ...

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