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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106 views

Why is the carrier suppressed by AM-DSB-SC modulation?

Lets say I have a message that is a sine wave at 1KHz. As I understand it, I can perform amplitude modulation by multiplying this signal with a carrier, lets say 10KHz, and this process is essentially ...
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25 views

5G NR standards equation

I'm currently working on the implementation of PRACH decoder for 5G NR. There are certain standards specified by 3GPP and we need to implement our module according to those standards. There is this ...
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2answers
111 views

What's the theoretical bandwidth?

A radio signal is sampled at $f_{s}=5512$ Hz, and $n=2^{14}=16384$ points are used in the FFT to display it as a spectrogram. The frequency resolution is $\frac{f_{s}}{n}=0.33642578125$ Hz/point, ...
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2answers
67 views

How do you get FFT for negative $k$ values?

I am reading a book (am a programmer so I suck at math) and it states that for a number of $k$-values that are symmetric around 0 (for example $k = -3, -2, -1, 0, 1, 2, 3$), we need to calculate $$\...
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1answer
120 views

FFT on a random signal

I have applied FFT on a random noisy signal (say for ex, on some stock data). Below figures shows input and output. Now, my question is, how to extract useful peaks (frequencies) from the output? Can ...
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1answer
50 views

Damped spring mass system - parameter estimation

I've tried to calculate the parameters of a damped spring mass system of the form $m~ y''(t)+d~y'(t)+c~y(t)=F(t)$ but I have some problems determining the mass m of the system. The damped ...
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1answer
69 views

Spectrogram of an executable binary [closed]

One of the approaches I have been searching so far is the application of utilizing Neural Network to classify Spectrogram images, which is heavily used in speech recognition. I am conducting an ...
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1answer
40 views

Non radix-2 FFT hardware implementation : zero-padding vs custom algorithms

I am an FPGA engineer with some DSP experience, facing the situation of implementing a 1023 points FFT in a spread spectrum demodulator. As a straightforward solution, I would zero pad to 1024 and ...
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35 views

FFT response for noisy signal, averaging the response and

I try to analyze a system's state with acceleration sensors by measuring the frequencies and amplitudes. Since a cheap sensor is used, I have a noisy signal in the beginning (up to 40Hz - see below). ...
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43 views

Cepstrum calculation with 5-smoothing zero padding

I am trying to compute cepstrum of a signal x An implementation of this in python is: ...
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155 views

Getting different spectrum from velocity, and position data using Omega arithmetic

I am solving a very long problem and one part of it requires me solving an ODE and computing FFT of the resultant data. Essentially I have a differential equation$\frac{dz}{dt}$ for velocity, from ...
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1answer
38 views

Coherent averaging of polyphase components of a signal

I want to subsample a multi-band signal to introduce controlled aliasing. My frequency components are uniformly distributed across the spectrum (comb structure) and occupy a relatively narrow ...
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2answers
48 views

Length of DFT defines whether I see the harmonic or the dominant frequency

I have a number of signals that are periodic. I use an fft transformation to obtain the dominant frequency of each signal. In order to increase the frequency resolution I zero pad the signal before ...
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0answers
66 views

Welch vs FFT squared in MATLAB [duplicate]

I'm trying to estimate PSD of a Binary signal with AWGN. Two inbuilt methods in MATLAB are giving me results one is Periodogram(Welch) and other is FFT squared. what is the basic difference between ...
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0answers
17 views

Formula for PSD across an axis of a 2D output

Consider a 2D stationary input $e(x,y)$ and a 2D real convolution function $h(x,y)$. Let $S=h*e$ be the result of the convolution of $e$ by $h$. If needed, we may assume $e$ is isotropic (spectrum ...
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4answers
161 views

Phase difference measurement of a signal sampled with two different sampling frequencies

I am working on phase interferometry for locating a transmitter. The direction of arrival of an incident wave can be estimated from the phase difference caused by the antenna separation as shown ...
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1answer
130 views

Difference between Fourier-Transform and FFT of rectangular pulse

I'm trying to find a link between the Fourier-Transformation of aperiodic Signals and the FFT of them. So to start with a basic example, let's take a rectangular pulse with width 0.1s and amplitude of ...
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0answers
57 views

fft formula convention

I try to code up an algorithm from a scientific paper where they solve a differential equation using Fourier transforms. In the paper, they use the FT convention $\rho(x_i) = \sum_{k=-m}^m r_k e^{i2\...
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1answer
40 views

Detect playback position in swept sine sweep

I am wondering what the most precise method is to detect the playback sample position of a sine sweep? The real playback sample position is unknown and an DSP with constraint computing capabilities ...
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1answer
61 views

Improving spectral response with lost downsampled data

I have a project that is resource constrained and must maintain a specific FFT length and small FFT bin width, down at baseband. My sampling rate is very high and needs to be downsampled to anywhere ...
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5answers
2k views

Is a Fourier transform a sound way to analyse a transient signal?

I am currently working on a project that involves analysing transient signals from sensors. While not actually part of the analysis itself, I discussed it with the team, and they are using an fft to ...
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0answers
128 views

How to interpret a 'noisy' Python FFT?

The following is a plot of the FFT of a noisy electronic component. It's not white noise, but is stochastic in nature. I used Python's matplotlib ...
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1answer
136 views

FFT strong signal in middle frequency bin

I've developed a radar that I'm using to determine the distance to remote objects. It uses a custom PCB with an onboard FPGA that performs the DSP algorithms. The data from it is then plotted on a ...
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1answer
119 views

Is it possible to find precise peak frequency using FFT phase shifts?

Been experimenting with FFT on a generated sinusoid and found something strange that doesn't seem to be described anywhere (though I may be missing something of course). A sinusoid that exactly ...
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3answers
477 views

I don't understand harmonics, why do they happen?

I don't understand why harmonics occur in signals. So if I receive a time domain sinusoidal signal at 10 Hz and I perform the FFT of it, I will observe peaks at 10 Hz, 20 Hz, 30 Hz, and so on... with ...
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1answer
50 views

solution on the time domain becomes “periodic” after the inverse fourier transform

I was trying to solve european option pricing problem using Conv method (introduced by Lord in 2008 https://pdfs.semanticscholar.org/0632/460bd50b2151f74ac40028df4cc60e73a884.pdf). The final step of ...
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1answer
75 views

Why does the FFT of a complex variable create negative frequencies?

So I have a demodulator that streams out X and Y values. I use a spectrum analyzer within this demodulator instrument which plots the |FFT(X+iY)| against the frequency domain, which shows up with ...
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36 views

FFT frequency-magnitude not correct when a positive gain EQ point is applied

I have a measurement system, which applies a log sine sweep as stimulus to a DUT and records the return signal. I then extract the impulse response, and perform an FFT on this to examing phase and ...
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36 views

FFT first frequency

I have some problems understanding FFT. If I know Fourier analysis frame (1024 samples) and sample rate (48 000 Hz), how can I find the first frequency of harmonic sines and cosines?
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31 views

Is fundamental frequency information present in speech-shaped white noise?

I am using a so-called speech-shaped stationary white noise, which means so much as a white noise that has been filtered to match the long-term spectrum of a female speaker. The way it was generated ...
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0answers
37 views

how to convert k-scale to frequency scale in FFT?

I have used fft(x) function in Matlab to perform Fast Fourier Transform on a given function and picture is the result. The graph you see is k, X(k). Now I am being asked to rescale frequency axis ...
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46 views

Some confusion about calculating spectrogram

I am new to DSP and i have a question because it is not the same as theory. I need to get spectrogram of wav file and feed it to CNN. I have used scipy.signal to get spectrogram. I know spectrogram ...
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1answer
108 views

Correctly scaling FFT of different lengths

I have been looking at using two FFTs of different lengths and displaying the output magnitudes on the same graph (a shorter length window for the higher frequencies, and a longer one for lower ...
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0answers
19 views

Transmitting image in certain spectrum without mirroring

I have a problem because I want to transmit string at certain frequency that is simple .png with 0 and 1. I simply take height and width of the image and scale it to the bandwidth and time. Then I ...
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0answers
79 views

How accurate is Python's FFT?

I am getting started with Python's FFT. I tested it on a signal that is a sum of three signals, two of which have an eigenfrequency of the grid, the third one does not (but due to large no. of data ...
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1answer
51 views

Peak to Average Power Ratio of an exponentially increasing signal

I am having an exponentially increasing sinusoidal signal. After sampling, I am dividing the signal into frames of length 128 and doing windowing operation with a hanning window of length 128. Then ...
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1answer
63 views

Why does an anti-symmetric function has zero amplitude at the center of an even length window

I am performing FFT on a real odd function and the resultant transform has zero amplitude in the last bin. Essentially if Y= rfft(X), then Y[-1] is always zero. I stumbled on this answer which says ...
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51 views

Audio Activity Detection and Classification

I am starting a new project. Actually, my real intention is to learn speech recognition but for warming up I want to improve in audio signal processing. In my project, I aim to record sounds except ...
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0answers
16 views

Multitaper F statistics

I'm having some problems interpreting the F-statistics output from multitaper analysis. To illustrate, the following code-snip in R performs multitaper analysis on the same sine-frequency but with ...
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0answers
194 views

Simple and Efficient FFT C or C++ code for HLS implementation

I'm working on my project and it's related to speech processing. I have to implement parts of the project on an Intel FPGA board using Intel HLS Compiler that converts C code to RTL code for FPGA ...
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0answers
19 views

Scaling factor for comparing spectrums obtained via Continuous Fourier Transform and Discrete Fourier Transformation?

Essentially I am trying to calculate the Bremsstrahlung spectrum numerically for magnetized plasma and want to compare the resultant spectra with the standard textbook spectrum formula for ...
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2answers
84 views

STFT window width vs. detectable Hz range

Assuming 44100 samples per second in a short 4-8 second-long audio .wav file, if I want perform FFT to detect the power spectrum, amplitude, and phase shift from 20 Hz to 10000 Hz (humans lose the ...
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1answer
102 views

FFT of white noise with different sampling rate

I have a question on how I should interpret the white noise power level (noise floor) obtain from FFT for different hardware sampling rates. I realized if I sample the same noise at different rates (...
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1answer
398 views

Scaling of the PWELCH function in MATLAB

I am trying to compute the power spectral density of a random signal using the PWELCH function in MATLAB. Since I think have not understood properly how Pwelch scales the PSD, I wrote a sample ...
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5answers
2k views

Can someone help explain what this FFT workflow is doing to my signal, and why it works?

I am working with a piece of equipment that does acoustic analysis. It does this by acquiring a time domain signal and performing an FFT on it to extract the amplitude and phase at a single desired ...
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0answers
29 views

Angle bins for FFT DOA estimation

I have difficulties to calculate my angle bins. After doing a fft over N points over the antenna elements I get N bins. For getting the angle of each bin I do the following: f_bin = (2*pi)/N*n (n ...
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2answers
633 views

Understanding the FFT phase spectrum with a simple example

I'm trying to compute the DFT using scipy's functions. I don't understand why the phase spectrum of a simple sine wave with 2 Hz frequency doesn't show $\pm\pi/2$ at the $\pm 2Hz$ frequencies. Instead,...
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1answer
74 views

Is it possible to reduce the complexity of radix-2 FFT if the input vector contains identical elements?

my question is about reducing the complexity of radix-2 FFT when the input vector has a specific structure. For an input vector of x with N elements, the complexity is given by O(N log2 N). My input ...
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3answers
93 views

FFT error when number of samples growth - Matlab/octave

I see when I increase number of samples, the imaginary error part of the FFT growth due to the error of sin(n*pi)!=0 where n is the index of the sample in Matlab or octave. Is there anyway to force ...
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0answers
22 views

how to calculate power spectrum of Gaussian noise from the known variance of it?

can someone explain me the following paragraph, i tried to understand it but i am not getting it exactly, Thank you ! Since you know the variance, you can predict the energy of the noise image, ∑x∑y|...

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