# Questions tagged [fft]

The fast Fourier transform is an efficient algorithm to compute the discrete Fourier transform (DFT) and its inverse.

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### Plot Frequency Spectrum of Binary Sequence in Matlab

I am new to Matlab and I am trying to implement a section of a published paper, the basic idea of the part that i am implementing is to show the frequency spectrum of camera aperture. The shutter ...
2answers
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### How to deal with the mirrored components of a FFT? And another question

I'm trying to simulate the behavior of my FFT spectrum analyzer, I am using Mathematica, but my questions are more conceptual than technical implementation of code...I hope. If we consider a simple ...
1answer
145 views

### Is discrete cosine transform differentiable?

Is DCT differentiable? I.e. is $\frac{\mathrm{d}\mathrm{DCT}(x)}{\mathrm{d} x}$ defined? I've seen a few implementations in automatic differentiation software packages, so I suppose the answer is ...
0answers
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### Time gating of FFT for audio Measurements or Multi Time Windowing

I am learning more about DSP specifically for audio measurement purposes. I can an app, where I can create a log sine sweep from start frequency to end frequency over a certain length. I can perform ...
5answers
11k views

### What are the problems with designing an FIR filter using FFT?

I'm trying to get an understanding of the relationship between an FIR filter designed from "first principles" using a filter kernel with convolution, and a filter designed in one of two ways using FFT ...
0answers
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### Causal bandpass using fft?

I would like to take a time series of several spikes or narrow Gaussians and bandpass using an ift/ifft together with a frequency domain mask to create a series containing band-limited spikes. This is ...
0answers
32 views

### How to generate wireless O-QPSK modulated signal in Matlab?

I am trying to create a small simulation where I would need to transmit a wireless signal from one wireless node to another and then transmit one more message back to node 1. Considering this is LR-...
0answers
24 views

### How to compare two 802.15.4 O-QPSK modulated digitals signals?

I am working on wireless sensors project and I am trying to simulate a transmission between two nodes. So let's say I have two nodes which transmit the message to each other, i.e. node 1 transmits ...
2answers
669 views

### FFT vs DFT Run Time Comparison (Complexity Analysis) in MATLAB

So we were given an assignment to plot the time taken by the FFT algorithm by MATLAB and a DFT algorithm written by me in MATLAB.G The expected output should have been the DFT algorithm following the ...
0answers
29 views

### Comparing two audio (Phone operator messages)

I have this two wavs. Same audible audio differente data. The audios are phone operator messages, so they are always the same. Wav:http://instaud.io/3Ezu Wav:http://instaud.io/3Ezw Using this ...
1answer
320 views

### What is a sliding window?

I tried to find the answer by my own but unfortunately I couldn't. Let's say I have the discret values of a signal which is 10s long. What is the FFT which is performed on a sliding window with ...
1answer
56 views

### multiplication in frequency domain equals convolution in time domain mismatch

We know that a convolution in the time domain equals a multiplication in the frequency domain. As per the article below, https://www.dspguide.com/ch9/3.htm In order to multiply one frequency ...
0answers
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### FFT of accelerometer signal: How to get a correct amplitude & noise reduction

I’m a student studying on vibration analysis & testing. I’ve performed low level sine sweep test of a simple rectangular PCB with clamped boundary conditions on two ends of it. That test was ...
1answer
149 views

### How can I get the power of a specific frequency band after FFT?

I need help with my matlab code. I have recorded EEG data and now I want to analyse it in matlab. I want to find the mean power of specific frequency ranges (theta: 4-8 Hz,alpha: 8-12Hz etc.). For ...
0answers
40 views

### Find a simple sine wave buried within noise, FFT or cross-correlation?

My recorded signal x = s + v, where s = A*sin(ωt) and v = noise. SNR < 1 or ~ 1. So the sine wave is buried under a lot of noise. I need to compare the relative amplitudes of s for each recording ...
2answers
86 views

### Attenuate frequency bin in FFT array resulting in artifacts [duplicate]

Am trying to remove noise for certain frequency bands by attenuating freqeuncy bins in the FFT array. However this results in artifacts to be formed, where there are clicking sounds in between each ...
1answer
32 views

### Extreme value at start of FFT proccesed signal

I have a signal with frequency of 1000 Hz, and it consist of velocities of an hot-wire. The measurements are taken behind a cylinder as air is blown on the cylinder. When i process the signal of each ...
1answer
47 views

### Prepare data for FFT

I'm reading the various FFT algorithms and the input consists usually of real and imaginary parts. The real data can be for example an audio input and the imaginary part should be the same sized array ...
1answer
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### What is the result of fourier transform of an image

I am new to computer vision and Fourier transform concept. I have examined some codes. In those codes, an image is performed Fast Fourier transform by using the function ...
1answer
88 views

### Units for a PSD from square of FT?

If I am looking to do a PSD plot on a signal $x(t)$ with units $m$ then the units I am expecting in the PSD would be $\frac{m^2}{Hz}$ but I can't seem to get this result from the following reasoning: ...
1answer
160 views

### FFT-based coarse carrier recovery for QPSK

An FFT-based coarse frequency acquisition block is being tested in GNU Radio. The algorithm used can be found on the GOES satellite user manual and is summarized in the figure below. The algorithm ...
0answers
17 views

### FFT time segment [duplicate]

When I use scipy.signal.spectrogram to calculate the spectrogram, with FFT size 2048, hop length 512, it return a time array which start with 1024 and increase 512 ...
0answers
17 views

### Finding subimage using correlation and FFT

For my assignment I have to locate subimages on larger image (simple OCR). I have text and sample image (e. g. single letter) and have to locate it's positions on larger image (which will be converted ...
0answers
24 views

### How to get PSD from frequency domain representation of time-series data [duplicate]

Let's say we have a realization (time-series data) of a random process. I take fft() of that to get its frequency domain representation. Then how can I estimate the PSD of this random process by ...
1answer
316 views

### FFT - mixed radix - bit reversal

I wonder what is bit reversal for mixed radix FFT. Is there any algorithm that compute the bit reversal for various mixed radix FFT? Here should be mention why I want that. For example if I have ...
0answers
11 views

### Wavelet Analysis Magnitude Scale

I am trying to plot magnitude against frequency averaged over a time window. To do this I make a morlet wavelet Filterbank. And multiply the dft of each kernel by the dft of my incoming data set. ...
2answers
227 views

### Simple $\sin(2\pi 1000t)$ Fourier transform in PSpice not behaving as expected

So I have this very basic circuit show below which I am simulating with PSpice. Now, when doing the Fourier transform of $\cos(2\omega1000t)$, I expect to see two impulses(one at -1kHz and one at ...
0answers
73 views