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

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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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56 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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35 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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15 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
26 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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26 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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21 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. Is there a method to find the amplitudes of the first few ...
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36 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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33 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
61 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 ...
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154 views
+50

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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41 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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23 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
36 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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39 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
30 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
33 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
77 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
64 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, ...
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1answer
75 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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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
42 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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23 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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101 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 ...
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2answers
33 views

Decomposing a DFT into multiple FFT calls

I'm using a good fast FFT implementation (vDSP) that will only work on power of 2 blocks of audio data. Now I have a problem where I would like to be able to apply the calculations to non powers of 2 ...
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47 views

MFCC help: Same sound, different coefficients?

Problem: I'm getting totally different MFCC coefficients for identical and near identical sounds like several finger snaps or several desk taps. What am I missing? I thought since the timbre doesn't ...
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2answers
37 views

Relationship of Fourier Transform and Spatial Directivity Pattern

I am reading over and over the Section 1.2 of most understandable mic array tutorial for me . A sound wave is dependent on time and space which can be observed in the great link. But I can't ...
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46 views

What does MFCC represent?

I have recently been involve in a project where we are looking for features to help with certain sound detection. MFCC seems to be widely used in the field. I know the routine to obtain MFCC via ...
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3answers
140 views

Processing Accelerometer Vibration Data With FFT

For a project I am attempting to use an accelerometer to measure vibration in an RC aircraft and determine frequency from the result. To do this I am using an MPU-6000 accelerometer sampling @ 1000Hz. ...
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41 views

Remove oscillations from an aperiodic signal using scipy

this might be trivial but nevertheless i've being strugling with the following problem for a while. I have two sets measured with a piezosensor. The signals are aperiodic in their nature. However, ...
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32 views

Fast Fourier Transformation using parallel processing coding for image processing [closed]

I'm now working in parallel precessing -and i want a full code for fast Fourier transform(FFT) written parallel processing Code for any image processing application
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1answer
44 views

Kiss fft does not work after giving it more than 32 samples

I am trying to take data from an accelerometer and apply Kiss FFT to the samples. I'm using a Freescale Kinetis FRDM-K22F board. I want to use 64 samples, but when I run the program I get an error ...
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27 views

Unable to obtain accurate amplitude using Continuous Wavelet Transform

I'm doing an analysis of pre-known signal (example in Mathworks), consisting of two sinusoids, one at 100Hz and the other at 50Hz. I applied CWT to the combined signal and the amplitude (~7 for 50Hz ...
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143 views

Get a N-FFT with two N/2-FFT already computed

After somme researchs on the web, I don't find the answer of my problem (or I don't understand it) and I hope this post will succeed. I'm working on a real-time FFT convolution algorithm (C++) which ...
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1answer
58 views

What is the minimum sampling duration to capture a given frequency?

Due to the Nyquist rate, you need to sample twice as fast as the highest frequency you want to measure. Then when you do a FFT the number of samples determines the number of bins and thus the ...
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355 views

FFT Result - which bins are useful

Which bins of FFT result are useful? For example I made FFT on 1024 real samples, and it produced result with 1024 complex samples. I read somewhere, the only half of that result is useful if input ...
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16 views

How can we verify CA-CFAR functionality with MATLAB?

How to initialize CA-CFAR/GOS-CFAR module in radar receiver? how can we verify its functionality in MATLAB? Thanks in advance.
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37 views

Most efficient phase linear x4 resampling algorithm

I'm working on a program in which I need to do the following about 20 times for each block of audio: - Upsample from 192 to 768 kHz (x4) - Clip - Downsample back to 192 kHz (/4) What I'm using now: ...
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27 views

What's the use case and explanation of frequency-domain subsampling?

In my solution to a certain problem I use subsampling in the frequency domain. Amazingly, it produces good results. Is it really that awkward to see subsampling in frequency domain? What the ...
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1answer
69 views

How to analyse Phase spectrum of 2D signals?

I am beginner in image processing. When I applied Fourier transform on two images say Lena and Cameraman etc., I obtained magnitude and phase spectrum for each one. I want to concentrate on phase ...
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79 views

DFT vs FFT: does odd number works for DFT only?

I am always confused between FFT and DFT. In both algorithm, it has been assumed that the signal is periodic (so my understanding is that, if you have a 20 sample point signal, and you do DFT or FFT, ...
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1answer
92 views

Is it possible to reconstruct an image using its magnitude only?

Let us take any image like Lena or cameraman. I know that when Fourier transform is applied on image,spatially global features like amplitude and phase are obtained locally. My question is whether it ...
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1answer
35 views

Phase is not linear in frequency domain after delay in time domain

When impulse response is symmetric around sample zero phase entirely zero. in = 0 , 0 , 0 , 0 , 1 , 1 , 1 , 1 , 0 , 0 , 0 -> This gives zero phase result As I know if I apply a delay in time ...
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59 views

Phase response of FFT in practice

As I know if the impulse response is symmetric around sample zero phase response should be entirely zero. The code below just set a rectangular window for vector "in" ...
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1answer
43 views

Beginner - use FFT to display spectrum/equalizer

At first, I want to say that I'm totally beginner in DSP and I don't have enough math education to understand Fast-Fourier transformation. I'm a programmer and I want to archieve something like ...
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86 views

Basic question about chirp signal

Suppose I generate chirp signal with the following python code: ...
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1answer
61 views

Efficient calculation of correlation function every N_th point

I would like to calculate a long correlation function of length say, 1e6 points. I have a prior knowledge that the correlation peak will be in point k*1000. Is there an efficient way to apply this ...
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1answer
59 views

Extracting amplitudes of components from FFT

I have a 4096-point FFT of a continuous pipe organ sound (no windowing). I wish to extract the relative amplitudes of the various harmonically-related sinusoidal components for voicing analysis. I ...