# 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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31 views

### How to find the "minimum spectrogram" across multiple recordings to extract a common audio signal?

The problem I'm trying to solve is that I'm trying to extract a "pure" version of a one-minute musical track that has been mixed together with voices speaking over it, over let's say 50 ...
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1 vote
55 views

### Why Does This Sliding Window Goertzel Filter Trick Work?

I'm reading an analog signal at a constant interval on an embedded device, and I want to extract a specific frequency component. Since the signal is continuously being read I want to constantly scan ...
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### Oversampling and decimation leads to slightly different result in frequency domain

I am trying to explore the effect of oversampling and decimation with the following Matlab code ...
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### Which FFT Window to use for data gathering of complete mastered songs - for AI

I have a novel technology that I developed, which I plan on incorporating AI beginning with simply recording a basic machine learning strategy of Input - Output for eventual training. In this case ...
34 views

### Convolution with the Inverse FFT of a Box Filter

I read through this post here on an example of filtering using the box function in fourier space. The example makes sense and I was able to follow it and implement it in Julia (I did in space instead ...
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### Phase shift between X and Y components of the same wave

I was told to post this question here, originally posted on Overflow. I have two signals, I1 and I2, which were acquired from a white light source in a spectrally resolved interferometer with a ...
56 views

### Is the analytical fourier transform of an exponential decay the same as the FFT of a time series of the same signal?

Analytical Fourier Transform of $e^{-t/2}$: FFT of a time series representation of $e^{-t/2}$: I'm trying to find the decay coefficiencts in tri-eponential decay signals, and as a logical starting ...
23 views

### How to setup the arrays to perfom fft at once?

I am trying to understand how to setup the arrays efficiently to peform the FFT at once. There are Lt samples for each Theta and ...
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1 vote
75 views

### Finding a certain animal from wildlife audio

I have a lot of audio data ~ 2TB, of 15 minutes being the length of each audio from wildlife, I would like to find a certain animal sound from that audio, the animal is Bullfrog (Rana catesbeiana), I ...
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### How to do spectral averaging to get satisfactory results?

I’ve been trying to implement spectral averaging as an experiment to familiarize myself better with FFTs and their uses for the past couple of days. Until I've hit a wall when I tried to replicate the ...
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### How single-tap equalization can be performed in OFDM for perfect channel estimation?

If I have for example IFFT length of 3 with cyclic prefix length of 2 and 3 channel taps, how can I illustrate the frequency domain equalization in OFDM? For example as far as I know, it's elementwise ...
37 views

### FFT Signal Analysis - Hardware Configuration

I have began working on a project that entails using an 1MHz Unipolar 12-bit ADC that has two inputs connected to a buffer opamp. One channel on the opamp is inverting, and the other is non-inverting. ...
1 vote
85 views

### Debugging a Haar wavelet transform in the Fourier domain

I'm trying to get a minimum-viable prototype going for a project on sensor fault detection using a scale-zero Haar wavelet (frequency-domain locality is not important). After some Googling, I managed ...
3k views

### Why zero-pad at the end of a signal?

I've been reading that to increase the frequency resolution of the DFT of a signal, you can add 0s at the end of the signal. But why is this the case? Why don't you add 0s in front of the signal ...
83 views

### 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 ...
1 vote
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### 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 ...
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124 views

### 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. ...
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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 ...
1 vote
109 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 ...
47 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
46 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 ...
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256 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 ...
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1 vote
151 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 ...
1 vote
190 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. ...
1 vote
28 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 ...
96 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 ...
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1 vote
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### 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 ...
32 views

### 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 ...
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40 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 ...
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### 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 ...
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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 ...
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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 ...
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 ...
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 ...
1 vote
101 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] ...
36 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 ...
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### 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 ...
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1 vote
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### 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 ...
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1 vote
48 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 ...
43 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 ...
1 vote
111 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 ...
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1 vote
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### 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 ...
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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 ...
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### 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 ...
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### 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 ...
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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 ...