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

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Interpreting the FFT results of a structural vibration problem

System: Cantilever beam type models, with an accelerometer on the end. The beam base is excited at various frequencies in harmonic fashion. This results in vibration in the beam. The accelerometer is ...
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1answer
13 views

Real-time frequency recognition in python

I'm a newcomer to signal processing, so forgive my ignorance. I'm working on a project in Python that will play a .wav file and pick out the dominant frequency as it plays. I've found a few examples ...
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9 views

period, amplitude and phase through FFT in matlab

I need to compute period, amplitude and phase of the signal from spectrum analyser. It looks like a sin wave. Since i am new to Matlab and also have limited idea about fourier transforms, I am looking ...
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1answer
26 views

Difference between real fft and complex fft with imaginary part of zero in fftw?

I have a real 2d matrix. I am taking its fft using fftw. But the result of using a real to complex fft is different from a complex ( with imaginary part equal to ...
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22 views

FFT frequency is always half of expected

I think I have a bug in my understanding of the complex FFT and it's leading me to get half of my expected frequency. I'm trying to calculate the frequency of an input signal of known frequency ...
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1answer
26 views

fftw log-log plot

I am taking Real time fft of an Audio Signal using fftw library. I take the output of the fftw signal on y-axis and plot it against the linear frequency bins on x-axis. I 've noticed that Spectrum ...
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20 views

How to calculate the frequency shift of FMCW transmitted signal and received signal using Matlab?

I generate a FMCW chirp signal between 18k-20kHz using Matlab, then sound the signal through the speaker in laptop, then record the reflected signal through the Mic in the laptop. What I want to do is ...
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16 views

ICI of zero frequency [on hold]

I am modelling inter-carrier interference (ICI) and I wonder how to account for ICI coefficients coming from zero (i.e., DC ) frequency?
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0answers
18 views

Representing and compartmentalizing FFT of audio sample into user friendly spectrum (need direction)

I am using the Apple accelerate framework to do some audio FFT analysis. Here is what I have so far and I want to make sure that my methodology is correct and I am indeed displaying appropriate data ...
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1answer
27 views

zero-phasing frequency components while keeping the same magnitude, in Matlab

How is it possible? I was thinking of taking just the real part of the DFT of my signal (isn't that zeroing out phases?) with real(fft(X)) but the magnitudes ...
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1answer
91 views

Why do we discard imaginary part of the phase spectrum?

Suppose I compute phase spectrum from the fftn function in MATLAB as ...
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4answers
129 views

Fastest implementation of fft in C++?

I have a MATLAB program that uses fft and ifft a lot. Now I want to translate it to C++ for production. I used OpenCV but I ...
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1answer
27 views

I want to calculate the period of the discrete time sequence from taking its fft(x,N). Can any one help?

This is my discrete time periodic signal, the time resolution of the samples is 0.2ms. And it's periodic after each 11 samples. So the fundamental period of the signal is 2ms or the fundamental ...
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3answers
55 views

EQ - Calculate the power per Octave of a signal through FFT

I'm working on a audio Equalizer, and I'm not sure if the way I obtain the power per octave of my signal is good. Here is the code I have : (I use the third octave bands, which is initialized earlier ...
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1answer
55 views

IFFT Synthesis from an empty spectrum

I'm trying to generate a sawtooth wave using the IFFT. I can do this successfully by first performing an FFT and then putting that analysed spectrum into the IFFT, however I would really like to be ...
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0answers
16 views

Getting better results from the Lomb Periodogram of a time series

Two times series were simulated, one with a period of 100 and the other with periods of 20, 40, and 60, for example: ...
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2answers
26 views

phase, magnitude, audio file and information

I've been doing some thinking lately. I know that for image files a larger portion of information is contained in the phase of the signal. How does that go for the audio? Does the same hold or is the ...
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1answer
46 views

Cross-Correlation to find the similartity of songs

I have been working on a problem where I am given two songs which are of the same category but there is a time difference between them. Eg. one song starts at x sec and other song starts at y sec. So ...
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36 views

Doubt related to application of FFT

I found this formula in a paper : http://ieeexplore.ieee.org/xpl/articleDetails.jsp?reload=true&arnumber=5655742 could someone explain the meaning of "j is frequency sample in the highlighted ...
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20 views

FFT analysis for series of different length

i have some data series in time domain which are in different length. i'm using FFT to transform them to frequency domain and now i want to calculate their average. Since their lengths are not equal ...
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3answers
135 views

How condition for existence of Fourier transform is valid?

The condition for Discrete time Fourier transform to exist for function $f(n)$ is given as $$\sum_{-\infty}^\infty |f(n)| < \infty.$$ In case of continuous Fourier transform the difference is ...
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1answer
36 views

How to find phase shift and process I/Q channel

I am currently working of 24GHz FMCW radar signal processing. The Module I'm using has 2 receiving antennas and each has 2 outputs (I and Q channel). So overall I've 4 channels. I'm using combination ...
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0answers
27 views

how to estimate the PSD using yule walker method in C++

I'm trying to estimate the PSD (in Yule-Walker method) from the FFT output in C++. First I convert the discrete signal in time domain to frequency domain using FFT. The FFT output contain the real ...
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1answer
41 views

FFT block exponent

I have a fixed point DSP library fft function that does not use a block exponent. I don't have prior knowledge of that implementation but whatever I could read online, my understanding is that its ...
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21 views

Detecting two changing inharmonic pitches

I have a recording of a newer type of siren that uses two pitches sliding back and forth in time. I want to be able to detect both of the pitches simultaneously or overlapping at short intervals. ...
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1answer
39 views

Conditions on $v \in \mathbb{C}^{n}$ such that the complex to real DFT is sensible

I'm using FFTW to compute some DFTs, and as a memory space optimization, you can give it a $v \in \mathbb{R}^{n}$ and it will return a $\hat{v} \in \mathbb{C}^{\lfloor n/2 \rfloor + 1}$ via the call ...
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22 views

Is negative frequency important in calculating Spectral Moments

A follow on question form this one (What is meant by "spectral moment"?) In answers to the above referenced question spectral moment is defined as: $$ m_k=\int_{-\infty}^{\infty} ...
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1answer
50 views

What is the reason for filtering out the negative frequencies of a signal?

I am reading this tutorial. Quoting the lines from the topic "Analytic signals and Hilbert transform filters": the corresponding analytic signal $ z(t)=x(t) + j {\cal H}_t\{x\}$ has the property ...
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1answer
22 views

How to determine relative distance between 3 in-phase transmitters by analysis of received signal

I would like to determine with high accuracy the relative distances between three RF transmitters a few meters apart by analysis of phase interference in the received wave, the receiver being at an ...
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1answer
51 views

Fourier Transform of a Pulse Train (Frequency Comb Simulation)

I am trying to take a Fourier transform of a femtosecond pulse train and plot the frequency spectrum. I followed this question and am able to create a pulse train and plot both the time and frequency ...
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1answer
22 views

Fourier Transform for speech signal [closed]

I need some clue on how to apply the Fourier transform to a wideband discrete signal like speech in Matlab. What I want to do is to apply the MUSIC algorithm to the speech recorded by a set of ...
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3answers
118 views

Reflecting negative frequency to positive frequency

I am trying to synthesize sinusoids by using window function in the frequency domain. It involves: In frequency domain, shift the window to center around the peak frequency To generate a DFT ...
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1answer
35 views

How do I perform Specral Analysis (FFT, Windowing, Detrending) on Sonic Anemometer Data?

I am having trouble with all of the forums that I have looked at thus far. I have one day's worth of Sonic Anemometer data. I want to see the specral analysis of this data. When the anemometer data ...
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1answer
45 views

How to get main frequency from digital signal

I have sampled digital signal with noise. I want to get main frequency of this signal how to do it? Currently it is smoothed by moving average. Is good way to make Fourier Transform an take the ...
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2answers
30 views

Discontinuity at the edge of Chebychev window

I am using Chebychev window for its narrow main lobe. The problem of chebychev window is that it has discontinuities at the edge, and it seems that Taylor window solves this issue. More detail: ...
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38 views

24GHz FMCW Radar Signal Processing Questions

I am using the RFE-3400 (from Innosent) 24Ghz Radar Transreceiver in FMCW mode. The output of the radar module has 2 channels of I/Q signals from 2 receiving antennas. My objective is to find the ...
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1answer
32 views

PSS convertion from Frequency to time domain

Hi I have a question regarding primary sync signal in LTE. It is generated in frequency domain and its length is 63. How to convert this signals frim frequency to time domain. Should I use IFFT? what ...
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1answer
92 views

How much deviation is acceptable in FFT calculations (using computer algorithms)?

It seems apparent that different FFT algorithms (e.g. Numpy.fft vs FFTS) produce slightly different results. I'm seeing deviations around 0.005 to 0.01 between programs. The reason for these, I ...
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1answer
64 views

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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1answer
264 views

Is it possible to do single vehicle tracking using Fourier transform?

I am working on a project in image processing which is based on importance of phase only reconstruction of a signal obtained using Fourier transform.For more information about phase only ...
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1answer
48 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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3answers
46 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
39 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
41 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
32 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
34 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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0answers
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
52 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
45 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
33 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 ...