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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21 views

How to downsample a fourier transformed signal?

I have a signal of length 100000 timestamps sampled at a frequency of 25kHz. First I apply a high pass filtering at (300Hz) and then do the Fast Fourier Transformation. Then the absolute values are ...
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34 views

What is the purpose of dividing an audio signal into segments and analysis each segment?

I read bunch of materials for extracting feature from audio signal and they all tell me to break signal into segments, why don't we analyze all the audio signal? I don't know what are the advantages ...
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36 views

Impulse response from frequency response in Matlab

I am trying to design equalization filter and therefore I want to define my own amplitude and phase response and then to obtain the impulse response of the filter. I thought that the output of the ...
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30 views

Convolution for audio, how to control amplitude?

I am implementation a convolution reverb method for audios array in Python using scipy.signal.convolve. I choose the fft mode, which essentially a product of the ...
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32 views

Why is it that the input to an IFFT is first reordered in an OFDM Modulator

I am back with my questions! I recently came across a paper titled "Low Latency IFFT Design for OFDM Systems Supporting Full-Duplex FDD" where they claim a new method of IFFT input mapping ...
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30 views

Does this FFT algorithm give correct IFFT when the input does not contain symmetry?

This FFT function is from Numerical Recipies in C and I am using it in my java projects. The source code is given below: ...
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+50

Using FFT for implementing a filter bank

I am trying to use Fast Fourier Transform (FFT) for decomposing an audio signal into 8 sub-bands according to this link but the problem is the frequency response of the result contains only the first ...
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31 views

Receiver function, frecuency domain deconvolution not giving logic results

I'm working on some code for receiver function method in seismology. For anyone one not into the topic, it's just a deconvolution of two time series (seismograms). This can be done in the time domain ...
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41 views

Mulitplication in Frequency Domain as a Similarity Measure of Audio Clips

I have an audio clip and I copy a 256-point part satarting at 10th second. Then I create a 256-point frame on the original clip. At every itreation, I calculate the DFT of the frame, multiply it with ...
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20 views

Direct path and reflections of ultrasound transmission

I am using the following system: Ultrasonic chirp signals with central frequency 100kHz are being transmitted using ultrasonic sensor. After the transmission through the medium(air/solid/liquid/...
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32 views

Does FFT on two samples from the same audio but with a very small sampling offset return the same results?

Using a single audio source, suppose I take two samples of the same length (say, 10s), with the same sample rate (say, 44100Hz), one just 1/3 sample length (7 microseconds) away from the other. Does ...
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55 views

Difficulty regarding grasping concept of fft butterfly?

The term "butterfly " is often used in association with fft texts But what exactly is a butterfly ?a matrix/group of i/o's is known as butterfly? Such as 2 input 2 output butterflies in ...
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Gnuradio scaling on Ubuntu issue

I have problem with scaling on gnuradio. When i use more than one WX widget - which shows parameters of signal - i can't see last widget. How can I deal with this problem - just to scale scopes, and ...
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48 views

calculate fft convolution for an LTI system given its input (in time domain) and its poles and zeros

I have considered taking the fft (MatLab) of the input (x) and create frequency bins for the first half (problems with an odd number of samples, tried solution zero paddings) and evaluate the transfer ...
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37 views

Confusion regarding plot of linear convolution vs fast convolution via FFT

I am reading Proakis Digital signal processing using Matlab, 3rd edition I am performing example 5.23 but i am not getting same plot/results as book although i am using almost same code First i am ...
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54 views

Why use PSD to analyze a signal instead of its Fourier Transform?

Let's imagine I have a perfectly known signal $s(t)$ and I want to analyze its frequency components. I noticed that mostly everyone would use the PSD of $s(t)$ to do that, instead of simply use the ...
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23 views

Fast convolution applicable;only circular or also linear/standard convolution?

Fast convolution is the convolution performed using fft Does fast convolution only works for circular convolution or also works for linear/standard convolution?
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32 views

Conjugate symmetry of the DFT of real-valued sequences

I have read about Fourier transformation that real signals are "mirrored" in the real and negative halves of the Fourier transform because of the nature of the Fourier transform. For ...
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86 views

Radix-2 vs Radix-4 FFT

What are the differences between radix-2 FFT and radix-4 FFT, Are the only differences following two: In case of radix-2 $N$ is a number that is a power of 2 and in case of radix-4 $N$ is a number ...
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28 views

What is the “Energy” equivalent of the Magnitude Spectrum

I have a semantic issue regarding the discrete spectrum $X[k]$ of a time domain signal with limited length $x[n]$, so we're talking about the FFT. Now, when I what to compare the bandwidth and ...
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Red noise estimation in power spectra. How to model the red noise component of data and derive corresponding confidence levels.?

I have generated a power spectrum using fft (python) and now I want to estimate the confidence levels with respect to red noise. Something like this: https://static-01.hindawi.com/articles/jcli/volume-...
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42 views

confusion understanding FFT butterfly diagram?where are 12 , two input butterflies?

https://www.alwayslearn.com/DFT%20and%20FFT%20Tutorial/DFTandFFT_FFT_Butterfly_8_Input.html I was reading above link and then i came across a confusing sentence, i highlighted it in attached ...
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13 views

What is the SNDR in ADC output

i have a sinus value at 80MHZ amplitude 0.5 with DC at 0.5 which was converted to digital sinus of values from 0-255. I have peformed FFT and found exactly a DC tone at 127 and 127 tone at 80MHz. both ...
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78 views

Auto Tune Shifting

So i have an algorithm that gets the fundamental frequency of windows, and can shift the pitch of each window as well (by a factor of x). For example. if x is 2 and the f0 is 440, the resulting f0 ...
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58 views

Cant find Doppler shift with LFM signal

Im stuck on this one. I hope someone helps me! Problem: I need to find Dopler shift with array of reflected chirps. I have bursts of chirps which then i sampled, and calculated fft. Im suposed to ...
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21 views

Zero peaks in fft data even after subtracting mean

I have a time series sensor data. It is for a period of 24 hours sampled every minute (so in total 1440 data points per day). I did a fft on this to see what are the dominant frequencies. But what I ...
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FFT question as it relates to Neural Networks / Supervised Learning Models

So I've been researching wavelet transforms and FFT. I want to feed wavelet transforms of a 1D signal in time into a neural net and train against a target variable at each time step. The idea being ...
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19 views

how twiddles are calculated in the code snippet below from ti.com?

I am trying to port a C code for fft/ifft to a DSP (TMDSEVM6678LE) from ti.com. In one part of the code it tries to calculate the twiddle coefficients as you can see below; however, I can't understand ...
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Does it make sense to apply convolution in the frequency dimension of a fourier transformed signal?

What I have is more likely a theoretical question. Since I am not from a signal processing background it is hard for me to grasp the issue in using convolution in the frequency dimension of a Fourier ...
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9 views

Calculate coherence ratio in HRV

According to this paper, coherence is assessed by Identifying the maximum peak in the 0.04–0.26 Hz range of the HRV power spectrum, calculating the integral in a window 0.030 Hz wide, centred on the ...
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55 views

Alternative Methods to Zero Padding

When using a sequential neural network to classify signals with their frequency spectrum, we would need to normalize the length of the signals to perform vectorization. The only method I'm aware at ...
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32 views

Hilbert Transform on split datastream produces phase flip

this is my first post here! I'm trying to do phase correction on a signal from a linear CCD (2048 pixels, 10bit per pixel, 250kHz linerate) in an FPGA. Therfore I need to generate an analytical ...
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18 views

FFT Multiple Response for time T

I want to do a fft spectral decomposition of a dataset, but the data has more than one sample for every time t. The data goes from the discrete years 1998 to 2010, each year has 20-30 points. Every ...
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34 views

What is the gradient of fft?

I have a time-series of length N generated by the following equation: ...
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41 views

How to interpret the window size and FFT size while performing FFT? [closed]

I have a discrete signal of length 98,000 samples and I am supposed to a FFT of the discrete signal with certain window size and FFT size. Can someone help me explain what is meant by the window and ...
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33 views

Zero-padding or Interpolation in 3D FFT

I'm trying to perform a FFT of a 3D regular grid and then compute the bin average (in spherical shell bins) of the Fourier transformed grid. The problem is that the resulted vector is very noisy as I'...
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PSD Accelerometer and Gyroscope

I used Xsens IMU and collected 1 Hour static data for accelerometer and gyroscope. I used the pwelch analysis in matlab to calculate the onsided PSD. The plots looks the following: How do I ...
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84 views

Why can we have non-integer frequency bins in FFT?

I am studying DFT/FFT and I'm very confused about one thing. I read online that the frequencies we can sample with DFT must be integer (Why does the frequency in the DFT have to be an integer?). Later ...
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Why does the frequency in fft plot of the baseband modulated signal isn't changing at the receiver

I have designed a transceiver system for cellular frequencies(800MHz). On the receiver side, I have converted the band signal to baseband signal through digital mixing. I have added the Inphase and Q ...
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15 views

How to extract the Freezing Index from Accelerometer data?

I'm working on a project to detect Freezing of Gait episodes for Parkinson's Disease patients, and according to this paper and other ones, extracting the freezing index which is "The power in the “...
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20 views

How to calculate FMCW Radar Chirp STFT?

I have received signal from FMCW Radar which is of the shape [128x64] = [Number of samples per chirp x Number of chirps per cycle] and i want to calculate the stft i am calculating it with stft ...
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56 views

Pitch shifting with bins creating large feedback

I am attempting to create a pitch correction algorithm. I started by performing a test. The test goes as such: Get WAV file Split it into bins of size n (512 in my case) Shift each bin by 2 semitones ...
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60 views

On the simplification using trigonometric functions

Assume I have a matrix $D$ whose its entries are as below : Where $A$ and $B$ can be written using using the trigonometric functions for (1) as: My question, Is it possible to simplify (1) more? ...
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FFT of a variable-frequency signal

I'm writing a software that read engine rpm during acceleration, using a recorded audio. To do that, I divide the record in small time-steps, and for each one I do an FFT, to know the rpm in that ...
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20 views

fft of a signal in the space at a fixed time

I have to do a fft of a signal in the space at a fixed time. I have always done fft of signals in time, so this is strane for me. In particular I have some difficulties in defining the Nyquist ...
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34 views

Construct IFFT from only the major frequencies of an input signal?

I have data which when plotted looks like the green line in the below image. The data is from the walking-motion of a reinforcement-learning-model in a simulation and therefore the values do not ...
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55 views

WOLA vs Simple Hamming Window on signal before FFT

Im working on a project in which I should FFT a signal coming into my FPGA from ADC. I want my FFT to show the peak values as clear as possible without the side lobes. The solution should be straight ...
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73 views

64 point FFT Hamming window interpolated to 720-point sequences

Can someone here explain the meaning of, 64 point FFT Hamming window interpolated to 720-point sequences and its inverse? 720 point is from 0 to $2 \pi$ or (0 to 720 degree). I get the 64 point ...
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27 views

Relationship of input-outputs in Hartley transformation based on few elements in a vector

This question is related also to that question HERE, but with further details and another issue I need to solve. Assuming we have a vector $X = [x_0,x_1,\ldots,x_N]$, its Hartley transformation is ...
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45 views

Relationship between input and output sequence in Hartley transformation

As you know that Discrete Hartley transformation is related to the discrete Fourier transformation, $i.e$, assuming we have a vector $X = [x_0,x_1,\ldots,x_N]$, its Hartley transformation is equal to $...

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