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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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Is it possible to transform a pointwise product into a convolution?

Let $A(k)$ and $B(k)$ be signals in the wavenumber domain. Is it possible to find a function $G(k)$ such that $G(k) \ast B(k) = A(k)B(k)$? Preferably a closed form solution. I tried the following ...
Lucas Bitencourt's user avatar
1 vote
2 answers
80 views

Baseband downconversion without imaging

I am a high school intern at a company employing heavy DSP and trying to learn the basics from the ground up. One feature of a test application I'm creating is the ability to zoom an FFT graph and ...
moltarze's user avatar
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2 votes
1 answer
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ECG analysis in MATLAB

I'm working on a little project involving digital filters and DFT, what I want to do is, given a sampled ECG, get the heart rate using power spectral density. I got the samples from this database. ...
minghierid's user avatar
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BERT (bit error rate test with ADC )

I'm trying to make a digital decoder. I sample a digitally modulated signal with the LTC2387, an 18-bit 15MHz SAR ADC. The carrier signal is at 2.1MHz, and is digitally mixed down to DC to obtain the ...
Abdel Djaferbey's user avatar
1 vote
2 answers
98 views

Linear convolution of a 100 sample time series and a 20 tap filter in the frequency domain

I came across this question on an internship application. For context, I'm three years into my bachelor's for electrical engineering right now. I have learned continuous and discreet convolutions, so ...
Ashik Islam's user avatar
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1 answer
42 views

Amplitude scaling for the FFT of a logarithmic frequency sweep

I have performed a logarithmic frequency sweep on a system from 1 Hz - 5000 Hz at constant amplitude and acquired the data at a linear acquisition rate of 10000 Hz. The frequency sweep reference ...
Nuno's user avatar
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0 answers
21 views

Help me to understand the input/output strides, number of transforms and input/output distance of 2D/3D data to perform DFT with oneAPI MLK libs

The computed excitation vectors of each basis function $m$ at level $\ell$ are just the samples on the sphere represented as $\zeta_m^\ell(\phi_i,\theta_j)$. These samples are interpolated to get ...
jomegaA's user avatar
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2 votes
1 answer
64 views

Confusion over deconvolution cost function gradient

A basic deconvolution problem is defined by the cost function $C(f) = ||f \star h - g||^2_2$, where $f$ and $g$ are unknown latent and measured images, $h$ is known kernel. I want to derive the ...
baronett's user avatar
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0 answers
29 views

Can I get a resonance frequency from FFT power spectrum result?

I'm going through vibration analysis of cantilever by using FFT device but impact hammer input data isn't showing for some reason. So instead, I'm trying to get the resonance frequency by acceleration ...
user72165's user avatar
0 votes
1 answer
45 views

FFT comparisons between g.USBamp software vs BCI2000 software

Update: I followed the instructions in g.USBamp Demo how to download the codes into Matlab (btw the product page is at https://www.gtec.at/product/gusbamp-research/ ) Here is the exact Matlab code ...
Jtl's user avatar
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4 votes
2 answers
249 views

Inverse filtering to undo a convolution blows up

Essentially, I'm writing a paper in which I want a figure that shows the effect of convolving an arbitrary curve with a Gaussian. Then, I want to show that you can deconvolve it by taking the FFT of ...
3edw's user avatar
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1 vote
2 answers
149 views

Why is reconstruction of window function from its DFT difficult/noisy when the sidelobes of DFT are higher?

I am able to use the DFT and IDFT formulae to get the DFT of a window and reconstruct it but only if the sidelobes is very low (or the main lobe is narrow) as shown in the image below: Why does this ...
RajaKrishnappa's user avatar
1 vote
2 answers
181 views

Taking an FFT of a signal that wraps around

I have an embedded application that does some phase modulation and streams back the phase offsets it's applying over UDP. I now want to take the FFT to see the spectrum of the applied modulation. ...
Ayush Agrawal's user avatar
1 vote
1 answer
19 views

How to measure the vibration of an object on a video shot at high speed camera?

I have a video fragment which I split into frames (pictures). I use them in pairs (1 frame with 2, 2 with 3, etc.) to find shifts on x and y axes (i.e. how much I need to shift 1 frame to make it like ...
tryingmybest's user avatar
1 vote
2 answers
89 views

IFFT return complex values in Matlab

I've been experimenting with the frequency sampling method for designing FIR filters. I created a low-pass filter that has a linear transition band. However, when I performed an IFFT on the frequency ...
minghierid's user avatar
1 vote
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35 views

Real-time Polyphonic Pitch Shifting - Time vs Frequency Domain Methods

I've been researching pitch-shifting algorithms both in the time and frequency domains with the aim of implementing a real-time polyphonic pitch shifter with minimal artifacts and latency (the goal is ...
Luke Galea's user avatar
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analysis the magnitude of fft of square pulse

It is pretty straightforward to scale the amplitude of fft's results by multiplying 2/Nfft (loosely speaking) to get the correct amplitude of signal components (except for the DC component), where ...
R L's user avatar
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0 votes
1 answer
37 views

Removing a repeated sound from an audio file

I have a pre-recorded sound effect (FX) that will be played every 5 seconds. Together with that, I also play a music track for a few minutes. The result is recorded. Now, I want to remove the sound FX ...
dz902's user avatar
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1 answer
57 views

Can the Constant Q transform be implemented more efficiently using an FFT?

I am trying to implement a Constant Q transform in code and was wondering if there was an algorithm that took advantage of the FFT to speed up the calculation so it can be used efficiently in realtime ...
tjwrona's user avatar
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1 answer
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Noise floor offset

This is from an FFT of a signal. The thick bands are supposed to be the noise floor. But why does it seem to have offset? What caused noise floor offset? Do you consider the peak at the left for ...
Jtl's user avatar
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How does padding two vectors for cross correlation affect result of time delay?

For example, i have two signals (x and y). If I zero pad both vectors at the end by length ...
skltynve's user avatar
2 votes
1 answer
2k views

Why does frequency sweeping double the frequency?

You can generate a signal with frequency f with sin(2*pi*f*t) where t is time. Yet, when I ...
Aravind Voggu's user avatar
0 votes
2 answers
38 views

Improving THD accuracy with unsychronized FFT

I am trying to use FFT to measure THD on a sinusoidal signal. My FFT window contains approximately four cycles, but my sample rate is not synchronized to the excitation frequency and it can drift ...
Campground's user avatar
1 vote
1 answer
95 views

computing convolution via zero, Periodic padding and FFT - confused about pad length and infinite signals

I’m trying to understand the answer to a test question. The question defines a new transformation for a discrete signal $x[n]$ which is defined for $0 \le n \le N-1$: $$X^c[k] = \sum_{n=0}^{N-1} x[n] ...
Piratemetaldrinkingcrew's user avatar
3 votes
0 answers
35 views

Expressing Frequency Bins as Period Bins

I'd like to change the x-axis of a Fourier transform frequency domain bar chart from frequency bins to period bins so that instead of displaying Hz or cycles/sec, I'm displaying sec/cycle; however, I ...
Data2Dollars's user avatar
0 votes
1 answer
37 views

Are integer multiples of a frequency in an FFT necessarily in phase?

I performed a FFT on a signal and the most prominent frequency at about 0.5 cycles/time only makes up about 6% of the total frequency distribution, which is pretty low for my purposes, so I was ...
Data2Dollars's user avatar
1 vote
2 answers
96 views

What Are the Units of a Fourier Transform? [duplicate]

I know that a Fourier transform (FT) outputs a distribution of how much of each frequency is present in a signal, but what would be the units of that distribution? It's not a proportion or a percent ...
Data2Dollars's user avatar
1 vote
1 answer
46 views

Is it possible to reconstruct the continuous frequency spectra from DFT/FFT?

Given the output of some FFT (lets call it X) with N bins (lets say 2048) is it possible to recover the values in between the bins in the same way that I can recover the values in between samples of a ...
little_brindle_dog's user avatar
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0 answers
39 views

Pixel Shift when using Fourier Downsampling

I am working on a Super-Resolution network, and want to try to use Fourier downsampling, different from the normally used bicubic downsampling as it relates to MRI imaging. I have tried using this ...
Christoffer Overgaard's user avatar
1 vote
2 answers
102 views

Excel FFT of Two Sine Waves Not Giving Expected Results

I did an FFT in Excel on a 440 Hz time domain sine wave, $y_1(t) = \sin(2\pi\cdot440\cdot t)$, and got the expected output in the frequency domain: a single-spike distribution with 100% of the signal ...
Data2Dollars's user avatar
1 vote
0 answers
46 views

Discussion on the relationship between the FFT magnitude spectrum and the corresponding actual amplitude

This might be a bit long, but it's a question that has troubled me for a long time, and I hope to get everyone's help. When studying signals and systems, we usually only pay attention to the relative ...
lilili's user avatar
  • 11
10 votes
3 answers
1k views

Why doesnt DFT Padding cause sinc like features

I'm new to the land of DSP so any incorrect terms please let me know. It seems padding the time domain signal can make the magnitude spectrum look 'nicer', the fact it doesn't gain any more useful ...
George kirby's user avatar
0 votes
2 answers
87 views

Jitter model does not behave as expected after FFT

So I'm currently trying to understand the relationship between jitter and phase noise. To help my understanding I did write a little simulation in matlab. I used this model in the time domain, relying ...
Maci's user avatar
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0 votes
2 answers
70 views

Peak FFT Frequency Off By One Bin

I used Excel's FFT feature to compute an FFT of a 440Hz sine wave that I also generated with Excel. The peak FFT value should occur at 440 Hz. Instead, it occurred one bin later at 528 Hz, so I'm ...
Data2Dollars's user avatar
0 votes
1 answer
84 views

What's Nyquist frequency in DFT?

I'm currently studying digital signal processing at university but I can't figure out what the Nyquist frequency means in the DFT coefficients, I know what the Nyquist frequency is in the sampling ...
minghierid's user avatar
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0 answers
46 views

Possible to combine and/or compare a swept Sine and a wide band noise signal?

I am working on a problem where two profiles need to be compared. One is a swept sine in $m/s^2$ (Acceleration) and the other is a sine-on-random signal composed of a swept sine $m/s^2$ and a random ...
SpillTheFFTea's user avatar
0 votes
1 answer
36 views

Can a bad quality sound be measured via THD?

I'm trying to create an app that measures the audio quality, this is ideally to filter out blown out or cracking speaker who has different types of distortions, what would be the best measurement ...
Priyank Joshi's user avatar
0 votes
1 answer
152 views

How to find frequency , location and phase of two sinusoid signal buried in noise?

There is a data set which has two different sinusoids buried in noise. Data record has following properties: A data records with a total data length of 2048 points. The sampling frequency is 100 Hz. ...
Thouhidul Islam's user avatar
1 vote
1 answer
48 views

Ignoring Negative Frequencies from FFT on Real Time Series Seems Inconsistent With Time Series

I ran an FFT on real financial monthly time series data. If I plot the FFT frequency domain output on the interval $[0, f_s)$, the dominant frequency pair peaks occur at $f_{A1}$ $\approx$ $0.02 \ ...
Data2Dollars's user avatar
0 votes
1 answer
47 views

Binning and Frequency for FFT on Financial Time Series Data

I'm trying to analyze financial market time series data, so are there any particular concerns in using FFT for that kind of data? The data seems to be relatively covariance stationary. My sampling ...
Data2Dollars's user avatar
0 votes
2 answers
73 views

How do you properly cut out negative frequencies from FFT of a real signal if it reduces sample size?

If a real time signal has $N$ samples, then the magnitude of its FFT will also have $N$ samples--half of which will have positive frequencies and half of which will have negative frequencies. The ...
Data2Dollars's user avatar
0 votes
1 answer
32 views

Frequency decomposition of forecast error variance

I think my question concerns statistical signal processing. I was referred to this site by a user at Cross Validated. I want to do a frequency-domain decomposition of generalized forecast error ...
Pavel Filip's user avatar
1 vote
2 answers
146 views

How does background noise affect the fft results for a pure tone

When I am recording a pure tone and conduct a fft, I receive a peak in the spectrum for this certain tone. Let's say the peak is 5 Now I am recording a pure tone with additional white noise. Does this ...
Stefan's user avatar
  • 21
0 votes
1 answer
54 views

Non-uniform FFT

I'm looking for a form of a FFT where the samples in the frequency-domain don't represent uniform spaced frequencies. What I would like to get is a frequency-domain with samples that are unevenly ...
wimalopaan's user avatar
0 votes
0 answers
24 views

Program to compare output and input streams to verify volume

I'm trying to wright a program to compare, two sound signals, output (speakers) and input (mic) streams and verify/adjust the volume. I'm using Microsoft Visual Studio C# forms project with the ...
djangocoder5925's user avatar
1 vote
1 answer
52 views

Is there any way to make the FFT more efficient for continuously sampling a signal?

So I want to continuously estimate the frequency content of a signal using the FFT such that at every sample timestep, I add a new sample to my current set of samples and remove the oldest sample in ...
Quéston Questioneer Esquerie's user avatar
0 votes
0 answers
18 views

How can i add overlap-add into this

Im new to DSP and i wanna know how i can add overlap-add into this to remove artifacts. ...
SignalWhisperer's user avatar
0 votes
1 answer
48 views

Zoom FFT shifting region of interest to be centered at zero Hz

So using this resource: https://flylib.com/books/en/2.729.1/the_zoom_fft.html I think I understand that the zoom FFT allows you to calculate the FFT for a region of interest with a lower order FFT by ...
Quéston Questioneer Esquerie's user avatar
1 vote
1 answer
61 views

Losing my mind over simple conversion of common Acceleration PSD-Units: g²/Hz to (m/s²)²/Hz

Because it causes confusion within my team I wanted to create a simple overview on how to convert from one PSD Unit to another. I know it is really simple but I've obsessed over it for a few hours. I ...
SpillTheFFTea's user avatar
0 votes
1 answer
42 views

Signal level from its FFT

Suppose I have the FFT of an arbitrary real audio signal z samples long. Is there a way to discover the signal level (intended as the largest absolute value of its samples) from the FFT without ...
elena's user avatar
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