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

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Fourier transform of an image

I am doing a project where I need to take the FFT and IFFT of a photo in MATLAB. There is a principle in optics where the intensity distribution from a lens is equal to the Fourier transform of the ...
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29 views

Whether the draback of Fourier transform will not allow to detect single moving object and avoid others from the traffic video?

I am working on a project in image processing which is based on importance of phase only reconstruction given in the answer by geometrikal in the link. Now ,I have detected moving objects from the ...
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1answer
21 views

Normalizing the magnitude of Goertzel Filter c#

I'm trying to detect some frequencies of 18Khz with sample rate of 44100 [samples/sec]. When I pass a buffer(~4500 samples) to the algorithm it returns a magnitude in a very strange range. Sometimes ...
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1answer
49 views

Reconstructed signal [on hold]

Someone can help me. I generate a gaussian pulse signal with $f=2 MHz$ and I apply the FFT. After that I select all frequencies above $-100 dB$ and I try to reconstruct the signal. I created this code ...
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3answers
45 views

FFT with day-periodic data

I have a collection of data: number of hours per day, over the course of several years. I want to create an FFT of this data. Since my sampling rate isn't seconds, but days, I think I have two ...
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1answer
36 views

Ways to identify if music has vocal timbres in it?

The human voice is singular because it has a specific frequency spectrum and fast transitions between vowels and consonants. What are good and computationally fast ways to detect if there is probably ...
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1answer
33 views

FFT “Brick Wall” Low Pass Filter Not Smoothing Output

I'll try to be as brief as possible. I have very limited signal processing experience. I have a data set that consists of essentially a big old sine function (with deviations from ideality), and lots ...
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1answer
30 views

FFT function of Gaussian pulse

I need gaussian pulse fft. I set the sigma of gaussian pulse 1e-10 and define the gaussian function in time and use the fft. as you know the amplitude of should be unit in frequency domain. but my ...
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1answer
21 views

How to set sampling frequency of an acceleration data set

I have a set of accelerometer readings in X, Y, Z axes obtained from an android based smart-phone. The data (in X, Y, Z) was recorded at different time stamps and there is no uniform time period for ...
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9 views

Energy-based speech recognition [duplicate]

I have a noisy recording with individual letters spoken. In a spectrogram view of the audio, the letters have higher energy. What can I use to isolate them? I'm fine with any tool.
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1answer
45 views

Slight crackle with overlap-add frequency-domain convolution

I'm trying to make an FFT audio filter using overlap-add but there's some slight rhythmic distortion/crackle in the output. I have an irSize (impulse response size) of 512 samples and a blockSize of ...
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1answer
33 views

Parallel Goertzel filters in C# [closed]

I have 2 frequencies in my application: $12000\mathrm{Hz}$, $13000\mathrm{Hz}$. I want to set a parallel Goertzel filters and every 100ms I want to take the bigger magnitude for detecting the tone ...
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1answer
23 views

FFT peak estimation: Zero-padding vs signal repetitioon

I am working on obtaining the vortex shedding frequencies behind a 2D square using CFD. Time-varying data is being extracted from a specific cell behind the square. I've written a little python script ...
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2answers
48 views

Noise removal from audio using FFT/Spectral editing

I have a noisy recording with some letters spoken out loud. I've noticed that the noise is easily recognizable when looking at a spectrogram of the audio. Is there anyway to set a power/frequency ...
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2answers
37 views

Drawing a Spectrogram off of FFT - what are the decibels relative to?

I am trying to draw a spectrogram from FFT data I get from audio files. The problem is that I can't figure out is what the yielded power (decibels) are relative to. I'm getting some arbitrary ...
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0answers
45 views

FFTW - Inverse FFT input data

I am trying to use FFTW function for IFFT: fftw_plan_dft_c2r_1d(size, out_cpx, out, FFTW_ESTIMATE). My goal is to input desired frequency response data and ...
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1answer
43 views

FIR Filter Design - obtaining FIR coefficients from frequency response

I would like to obtain FIR filter (low-pass) coefficients from a given frequency response by using C++ to develop algorithms. I have read at http://iowahills.com/B2PolynomialFIRFilters.html, that, if ...
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1answer
103 views

Compare phase and magnitude spectrum results of 2 Images [duplicate]

I have read that from Fourier transform we obtain magnitude and phase spectrum. The magnitude spectrum tells you how strong are the harmonics in a image and the phase spectrum tells where this ...
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25 views

How do you find the position of when a signal changes frequency?

Suppose I have a signal which varies between two frequencies (which represent a stream of binary data). I think this is called BFSK. I have the entire signal already sampled. Let's say each 'bit' ...
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2answers
69 views

Key detection Dance Music inaccuracies - matlab

I have been working on a project with a vide variety of functions for DJ'ing. I am nearing the end, however, the accuracy rate on the key detection part of it is not pleasant when fed tracks of Dance ...
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1answer
104 views

What is the right way to extract particular frequency phase information from FFT?

Signals acquisition: Two proximity sensors are positioned Orthogonal to each other. These would be measuring the vibrations of a rotating shaft. Problem: Each of these 2 signals has two dominant ...
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1answer
69 views

FFT of signal with starting value zeros

I have a signal, ...
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1answer
66 views

DFT and FFT application in signal processing

Can anyone give me some hints to solve this problem
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Vigner Ville Spectrogram vs Filter Bank Spectrogram Comparison, please interpret

Here is an image of two spectrograms of the same bird call. Please help me to understand the results and the advantages and disadvantages of both methods. I Quote: "The WVD exhibits the highest ...
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1answer
44 views

How can I detect known frequencies using most efficient algorithm

I have a set of ultrasonic frequency that I am playing and I want to detect these particular set of known frequencies. I have already used fft but it is quite processing intensive and I am facing ...
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1answer
30 views

Averaging Multiple Magnitude Spectra

I'm currently trying to implement some of the methods found in this paper on intelligent equalization - http://www.aes.org/e-lib/browse.cfm?elib=16792 - The first part of the process is to build a ...
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27 views

Length and spacing autocorrelation with FFT

I have calculated, with FFT and A-FFT, the autocorrelation of a discrete signal (coming from an integration) with spacing $\Delta T$ composed by $N$ samples padded to $2N$ with zeroes. What is the ...
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1answer
191 views

What is the most precise frequency analysis spectrography algorythm?

Everyone uses Fast Fourier Transform, which is fast at the detriment of precision. The input audio has sample accuracy and the FFT has 1/64 sample accuracy. What algorithms can output high resolution ...
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1answer
93 views

Power Spectrum in dBFs

I'm trying to get the spectrum of my signal in dBFS units. I'm not sure what is the refernce that I should devide by. I computed the power spectrum as follows: 1) FFT normalized to the number of ...
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2answers
144 views

Signal decompositon

I am not a good in writing algorithm but please follow below steps 1.There are 4 1D sinusoidal periodic signals.3 of them are given by \begin{cases} x(t)=4\sin(10\pi t) \\ y(t)=8\cos(20\pi t) \\ ...
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1answer
264 views

Is it only me or matlab's periodogram's function is confusing?

I am really confused with matlab's periodogram. First of all, it says in the documentation that its unit is "dB per unit frequency". What does that really mean? I just don't quite get it. Second of ...
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2answers
259 views

Fourier Decomposition

Hello everyone have a look at this video of Fourier Decomposition of an image(otherwise you can also refer the image which shows few plots of different extracted waves from an image) . We also know ...
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2answers
127 views

Finding the Harmonics contained in an Image?

I am beginer in image processing. Any signal whether it is 1D,2D or any multidimensional signal can be represented using combination of number of sine and cosine wavesforms (harmonics). Similerly any ...
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55 views

How do I interpolate between bins on an FFT in python?

I have four frequency peaks, which I have after applying FFT. Now I want to know precise values of these frequency peaks. there are different interpolation methods. How can I use this method of ...
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71 views

Dominating frequency in a “clear” 50 Hz signal

I am trying to find out the dominating frequency of a signal with a frequency of 50 Hz (sampled at 200 Hz - every 5 milliseconds). The python code I am using to do this is the following (based on ...
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24 views

FFT for Object Recognition, what distance do you recommend me?

I'm trying to make a custom CBIR which describes one image and finds the closest ones. I wanted to use FFT to describe the pattern that it has, for example "checkerboard", "lines" or "dots". We ...
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2answers
40 views

Harmonic estimation from a single note

I have a recording of a single note played several times on a violin. I'm working with Matlab to estimate the amplitude of the first N harmonics. I already know which note is played but there can be ...
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0answers
47 views

DTFT of beat signal with shift due to multiplication

I am simulating a FMCW radar (Ramp signal is used for transmission)and I have created the transmit signal from matlab FMCW model ...
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0answers
23 views

Orthogonality test on fixed point FFT

I have tried the following methods to test the orthogonality on Fixed point FFT implementation. FFT: Y = A*x, where A = FFT basis and x = input, Y= FFT output If the input (x) is set to A-1(A ...
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1answer
83 views

Intuitive explanation of cross-correlation in frequency domain

According to the cross-correlation theorem : the cross-correlation between two signals is equal to the product of fourier transform of one signal multiplied by complex conjugate of fourier transform ...
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1answer
104 views

Shift in Time-Domain after FFT-Convolution

To my understanding, multiplying a signal in the frequency-domain is equal to a convolution in the time-domain. I wrote a small python program, but i always end up with a shift in the time domain. ...
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2answers
41 views

Simulation of a pressure field developed by a song

Greetings! What I am doing: In short, I want to write a program that is fed a song as a wav file, and spits out an animated contour plot indicating the relative pressure/loudness/quantity indicating ...
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0answers
17 views

Implementing a Number Theoretic Transform (Fermat number transform--257). Should I consider alternatives to a radix-4 cooley-tukey?

This is kind of a comp sci question, but I figured I could use some input from FFT experts. I've already got a radix-4 cooley-tukey implementation of the NTT briefly described on page 9-10 of ...
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2answers
33 views

How can I get maximum complex value from an array of complex values(524289) in python?

I have an array of complex values. Actually this array contains fast Fourier transformation fft values. now I want to fetch maximum complex value from the array. Thanks
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30 views

Audio output distorted with any FFT Windowing other than rectangular

For an experiment i have a simple application that takes a quadrature signal from a radio and then does the following: Complex FFT -> Inverse FFT -> Cartesian to Polar -> audio out If I tune the radio ...
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2answers
61 views

recovering phase of sine signal from FFT

I have a simple sine function as $sin(2\pi ft + \phi)$. I want to obtain the phase signal $\phi$. I tried to use FFT to calculate $\phi$. In matlab I do the following ...
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0answers
29 views

What is the preferred method of aggregating audio FFT data given variable-size frequency bins?

I am coding a program which uses a FFT to process audio data. I need to aggregate the FFT output into three bins ("bass", "mid", and "treb") determined by two arbitrary frequency values. The end-goal ...
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2answers
125 views

filtering in frequency domain

I am performing decorrelation of two channels of audio using all pass filtering. The two all pass filters for two channels are of very high order (>1000 but with not all coefficients non zero). I have ...
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180 views

Can anybody explain about phase shift and phase spectrum terms in case of multidimensional signal?

I know about phase of a 1D signal. But when I go into higher dimensions like 2D,3D etc, it becomes headache to grasp the concept. What are the terms phase shift and phase spectrum mean in case of ...
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2answers
182 views

Whether phase congruency and phase coherence terms are same or different?

I am beginner in Image processing.I am studying the importance of phase in signal.Can anybody explain what is phase congruency ? Also,I am confused between terms i.e. phase congruency and phase ...