# 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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### Removing DC Offset (via removing mean) of input and output signals affects their coherence

I have input $x$ and output $y$ signals (fs=10 Hz, length N=10800). I have removed DC offset via the following equation: $x_{normalized} = 100 \frac{(x-\bar x)} {\bar x }$ where $\bar x$ is the mean ...
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### For SNR calculation, should I use FFT|X+iY| or FFT|R|?

I use a demodulator that outputs X and Y quadratures, with the R and Phase which can be calculated. For SNR measurements, when plotting the FFT to find the SNR a signal at a certain frequency, ...
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### Periodic Data Modeling

I am new to DSP and trying to learn its basics. I have a periodic data set (Y) and am trying to determine a numerical model which fits to the data set. I intend to find an equation which - Can ...
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### Use of Tukey window and its effect on a graph

I am trying to minimise the noise in a spectrum of a variable. I am trying to use the suggestion of my advisor, who told me to divide the time history in equal parts, to do the FFT of this time ...
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### Zero padding in frequency domain, any tricks to speedup?

there are many situations when one has to carry some operations on spectra, like splitting a spectrum Z wide in two Z/2 spectra, or vice versa merging two Z sized spectra in a 2Z sized one. The only ...
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### Understanding outputs of image Fourier Transform in Numpy

I am trying to understand the meaning of FFT outputs with respect to images. Take a look at the following example: ...
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### Spectral filtering

I am working with a STFT spectral processing toolkit I wrote in C, now focusing on a module for spectral filtering. In its first implementation, the module simply multiplied an user drawn spectral ...
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### How to detect overlapping peaks in FFT?

I am working with a modular spectral processing STFT toolkit I have written in C. I often need to carry spectral peak detection and analisys (frequency estimation, peak displacement, etc) but I am ...
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### How to manually implement convolution with FFTs?

I'm trying to manually implement a convolution using FFTs and it isn't working as expected. I know I'm probably missing some subtlety with padding, shifting, or conjugation, (all of which I've tried ...
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### Different representations of frequency space of 2D image FFT

I'm learning images processing using FFT. In my test example provided below the input pixel values are clamped 0-1 (0-255), but I do eventually want to process floating point heightfield pixel values....
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### Splitting audio into multiple audio based on frequency range in Librosa

How can I separate an audio signal into multiple audio signals based on frequency range? I used librosa.display.specshow to vi
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### 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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### 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 ...
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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### 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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### 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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### 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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### 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 ...