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

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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
27 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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0answers
25 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
57 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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22 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
98 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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2answers
126 views

Physically what is phase term means for multidimensional signal?

I want to ask very basic question related to multidimensional signals like an image or a video signal. What is phase term means for multidimensional signal like an Image or video signal(like for ...
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2answers
148 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 ...
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1answer
32 views

Calculate amplitude of noise added Sine Gaussian signal from frequency domain

How to calculate the time domain amplitude of noise added Sine Gaussian signal from corresponding frequency domain. Here time domain amplitude is 2. How to get this from frequency domain. ...
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1answer
56 views

Applying Gaussian Blur in frequency domain

Please see second update I'm trying to implement gaussian blur in frequency domain using c#. Those are steps that I'm doing: Load bitmap. Split bitmap into separate color channels. Convert every ...
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4answers
370 views

What's the exponential term in Fourier Transform mean?

We know that Fourier Transform $F(\omega)$ of function $f(t)$ is summation from $-\infty$ to $+\infty$ product of $f(t)$ and $e^{-j \omega t}$: $$ F(\omega) = \int\limits_{-\infty}^{+\infty} f(t) \ ...
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1answer
39 views

How do I obtain the frequencies of each value in a 2D FFT and what do they mean?

My goal is to analyze the frequencies in an image representing water simulation data before and after, for example, a Gaussian filter. The direction of these frequencies is not important to me. ...
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1answer
64 views

Spectral leakage issue cannot solved using windowing

I am designing a frequency lowpass filter using FFT&IFFT. My test data is a time series with a large DC component (the pink curve). Before the FFT, the time series was detrended (curve fitting) to ...
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2answers
42 views

Melody/Vocal extraction

I'm new to the whole DSP area, but I've built a program which plays music and does FFT to produce some cool visuals for the music in realtime. The FFT algorithm I chose was from a C# library called ...
-1
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1answer
43 views

fft2 of interferometric image - how to interpret the result in term of dominant frequency

I have an interferometric image which shows fringes at a certain frequency, basically a dominantly periodic signal overlaying the information that I want to extracthere are the fringes that I want to ...
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1answer
26 views

MFCC from DFT (FFT)

I want to write an speaker recognition application (based on some password recorded few times for the authorized person). I've decided to do it with C++ and BASS library (http://www.un4seen.com/). I ...
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0answers
27 views

Overlap add / overlap save using FFTW

I'm working on a realtime FFT processing algorithm in C using PortAudio. Currently I'm just trying to test if I can do OLA / OLS in (semi) real time using FFTW. I'm getting some distortion in the ...
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0answers
33 views

Help with Fourier transform [duplicate]

Firstly I must say that I'm beginner in field signal processing. I'm familiar with Fourier series but I have some hard times in learning Fourier transform. Why we use it? What's purpose of Fourier ...
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0answers
15 views

Interpolation of two different FFT spectrum

I have two almost periodic signals which are steady-state response of a nonlinear system for two different input, say, 10 Watts and 15 Watts. I perform the FFT of the signals. Does it make any sense ...
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22 views

Is this the DFT matrix?

I read a paper that said that the $K$-point DFT matrix is the following Is that correct or should the elements be more like $$e^{-j 2\pi/K}$$ i.e, isn't the minus sign missing? Also does anyone ...
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1answer
34 views

FMCW SAR chirp return from target modelling

I have to Model a chirp signal that was return from a Distance D from target and then multiply with the reference transmitted signal. Which will give me beat frequency signal and then fft to get the ...
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0answers
23 views

Finding periodicity within sequence of time hacks

I have a series of time hacks for various events that have occurred. Some of these events occur at regular intervals (+/- some small variance) but I do not know what those intervals are and would ...
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35 views

Feature Extraction from Accelerometers for classification

I am looking into algorithms/techniques for feature extraction for accelerometer data - to then be used in classification. FFT is incredibly popular, however would this work on accelerometer data? ...
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1answer
53 views

Real time fft/ifft processing

when manipulating a live stream of audio data in the frequency domain, I've heard you need to do fft / ifft in small chunks, say 256 samples at a time. I've also heard you need to somehow employ a ...
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1answer
36 views

Convolution in frequency space with fft and ifft -> num output samples?

Let's say you had two 1 second sound samples at 44.1khz, and you wanted to convolve them in frequency space. You FFT each one to get two arrays of complex numbers that each have 44100 items in them. ...
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3answers
75 views

Amplitude of frequency in MATLAB FFT

I am trying to extract amplitude of specific frequency in Matlab FFT. Is it possible to use the abs(mag)... But I do not know in which sample to look for ...
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2answers
38 views

Fourier Synthesis With Varying Frequencies Over Time

I'm doing some fourier synthesis by making bins of complex numbers, filling them out with the amplitude and phase information and using IFFT to turn that into time domain samples. I'm able to make ...
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0answers
16 views

Sinogram Fourier Analysis Doesn't Show Clear Bow Tie Shape

I'm working on finding the center of rotation of a set of test tomographic projections in order to perform 2D reconstruction. I'm trying to implement the algorithm to find center of rotation as ...
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1answer
29 views

Deriving Time-Series Data from PSD when the Inverse Fourier Transform doesn't converge

So I'm trying to get some sample time-series data from pink noise (PSD: $S(f) = 1/f$). However, when I try to evaluate the Inverse Fourier Transform integral $\int \frac{1}{\omega} e^{j \omega t} dt$ ...
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1answer
30 views

Determining Power Spectral Density from Autocorrelation Function and Time-Series Data

So I think I've confused myself a bit here. I know that taking the FFT of time-series data (wind velocities, for example) yields a power spectral density. However, I just read that taking the Fourier ...
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2answers
42 views

Finding amplitudes from FFT data of a 2D image

I'm working on experiments with 2D - wrinkled surfaces. Basically I am getting a bunch of images like this. This example is hand-made. Edit: The test image was made by sampling a cosine function ...
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0answers
45 views

How to define cyclic frequency for cyclostationary signal in terms of signal parametrs?

I am trying to detect cyclostationary signal. For that it is required to know its cyclic frequency. But I am unable to figure out how it can be related to signal parameter. Is it possible to define ...
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1answer
41 views

method to detect frequency sweep in audio

I have search a bit to try to find a similar questions, but I have not been able to find any leads. There are techniques to programmatically detect steady tones in audio, such as the Goertzel ...
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1answer
25 views

Implement Fast Hartley Transform

I'm trying to implement a simple FHT on .NET platform myself. I follow this document: Optimized fast Hartley transform for the MC68000 with applications in image processing. In the page 20th, equation ...
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1answer
80 views

aliasing to a 50 Hz sine wave sampled at 5000 Hz sampling rate?

I sampled a 50Hz sine wave (its not perfectly a sine wave, it's a data coming from current sensor using Arduino). Using real time graphing technique by sending the data from Arduino to the PC I ...
2
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3answers
167 views

FFT on non-uniformally sampled signals

Most fft tutorials use sinusoidal signals for demonstration, which makes the user already know what the fft is supposed to give as an output, but what about real time signals where we don't have any ...
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3answers
72 views

How to add pitch-shifted version of signal to itself?

I want to write an algorithm to add pitch-shifted version of audio signal to itself (like Electro-Harmonix POG does). And I need to do it in realtime. How to implement it? My guess is: break signal ...
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0answers
28 views

Compare two voices and outline their similarity

I am trying to develop an application which records the voice of someone through a microphone. I will have a preset recorded voices for the same words. I then need to compare the real time recorded ...
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1answer
46 views

How should I select window size and overlap?

I'm new to DSP and I have a wav file with a number of different frequencies playing at different volumes. I'd like to plot the power of the 350Hz frequency signal at each point in time. The source is ...
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40 views

How to process the .wav file to get meaningful information like the number of inhales/exhales

The plot of the data from the wav file. Link to the sound file - https://drive.google.com/open?id=0BxAPlY66uX7qWWtDZUw3WkpjSGs&authuser=0 Also the FFT plot is like this I am new to the field ...
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1answer
32 views

Do I need an overlapping in STFT if I want to play the signal back?

I want to write an algorithm to implement a pitch-shifter, like in this article: http://www.guitarpitchshifter.com/matlab.html. And I need to do it in realtime, not with a signal already defined ...
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1answer
34 views

How to implement the imaginary part of FFT equation applied to a signal in computer/C++?

I am trying to apply FFT on a time domain signal in C++, however I am having trouble with the imaginary part i.e square root of -1. In the FFT equation we have, $$X =\frac{1}{2\pi}\int_a^b x(t) \ ...
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1answer
38 views

Remove checkered noise from an image

I'm trying to remove what looks like a checkered noise pattern that has been added to an image. Comparing the 2D FFTs The one on the left is the original, while the middle one is the corrupted ...
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2answers
95 views

Perform Convolution in Frequency Domain Using FFTW?

I'm trying to convolve two signals $x(n)$ and $h(n)$ in C by using the FFTW library's functions to perform a Fourier transform on each, multiply the appropriate complex components together, and take ...
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1answer
84 views

matlab fft phase response square wave

I am new to phase analysis, recently I have been trying compare the phase between the input signal and output signal of a system. From the code below, I simulated a square wave and plotted the phase, ...
2
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1answer
79 views

What does the word 'bin' mean in the context of FFT's?

Everywhere I read about the FFT, I read about frequency bins. I can't find anything about what is precisely meant with 'bin'. What I wonder about is if this is actually meant to imply that the FFT ...
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0answers
9 views

z-transform for baseline correction for an ERP signal for performing FFT

For a time frequency analysis of an Event related potential (ERP) signal I want to perform Baseline correction. For my signal power is too high for the regular subtraction method. Can I use ...
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1answer
47 views

why is the plot of the PSD of this autocorrelation function oscillating?

I was doing an exercise trying to compute the PSD of the following discrete autocorrelation function: \begin{equation} r_x(m) =(1/2)^{|m|} \end{equation} In this simple matlab code that I came up ...
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26 views

How does we choose parameter in SPECTROGRAM(X,WINDOW,NOVERLAP,NFFT,Fs)

I am facing problem in SPECTROGRAM(X,WINDOW,NOVERLAP,NFFT,Fs) How would i choose Window, Noverlap,nfft parameter for spectrogram of children voices sampled at ...
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3answers
106 views

FFT bin interpolation for low frequency with DC offset

I have a noisy signal in I/Q format with a peak frequency that constantly changes between 0.5Hz and 4Hz. The sample rate is 64Hz. I want an output showing the current peak frequency with a maximum lag ...