# Linked Questions

16 questions linked to/from Why is the FFT "mirrored"?
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### 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 ...
9answers
81k 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 ...
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### 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 ...
2answers
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### 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, ...
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### 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: ...
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### 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:...
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### 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 ...
2answers
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### 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: ...
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346 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 ...
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### 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 ...
2answers
280 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 ...
1answer
196 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: ...
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### 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 ...
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### 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 ...

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