# 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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### How do you sub-sample an FFT?

I'm currently trying to understand this paper on a Sparse Fourier Transform. On page four, there is a section on a sub-sampled FFT. The purpose of this section is to show that you can compute a sub-...
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### On the channel estimation based on vector

I have a matrix $X$ of size .i.e $(8,8)$ with $M$ columns and $N$ rows. Suppose I took it's $iFFT$ column wise resulting matrix $x$ of size $(8,8)$ too, $x = F^HX_{(:,m)},$ ...... (1), where ...
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### 2D DFT in image processing in python

I try to compute 2D DFT in a greyscale image with this formula: I write the code bellow with python ...
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### How to develop a spectrogram (2D array) from audio signal?

I have developed a spectrogram in Python using Scipy.Signal.Spectrogram. But I need a complete understanding of data. Here I am not asking about plotting and color ...
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### Understanding FFTs for simple Sin / Cos

this is my first question in this forum, and although I read several threads on this side and googled a lot I could not find the answer to my question (maybe it is too basic)? For anyone reading this ...
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### Handling stride>1 in FFT-based convolution

The Fourier transform of the convolution of two signals with stride 1 is equivalent to point-wise multiplication of their individual Fourier transforms. I need to perform stride-'n' convolution using ...
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### How to get coordinates(x(time),y(frequency)) of spectral peaks from spectrogram?

I have created this spectrogram from a wav file. Please have a look: As it can be observed clearly that my somewhat spectral peaks are visible. I want to get the x = time, y= frequency of these ...
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### Remove known sound from signal

I'm currently getting FFT values from the music playing from a user's PC. However, my application also generates noise which interferes with the FFT data as my app's sound is also coming out of the ...
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### Pitch correction using Fast Foruier Transform [duplicate]

I am very new to digital signal processing and I have a project about audio programming. For the project, I wanted to try to make an Auto-tune like effect. I started by experimenting on the signal ...
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### Noise floor flatness in IQ FFT window

I am doing a simple $P_{in}$ - $P_{out}$ linearity test for my RF generator/receiver system. The generator provides an IQ modulated CW single tone with $P = - 80dBm$ at 1 GHz. If we look at the RF ...
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### creating this famous basic nyquist theory photo

Hello i ha built this code which create a only one replica of the data, how can i create the whole photo shown bellow of many cycles as shown bellow? i read in the internet that zero padding could ...
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### What's wrong with my STFT implementation?

I'm studying the linear convolution for achieve more complex results in Audio FX. My main goal is to implement a realtime convolution between two stream of sound in live perfomance (for example Sound ...
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### Circular convolution of real signal N by N/2 sized complex IFFT

There are two related questions with good answers; for calculating the forward FFT in N/2 values, and calculating inverse FFT from N real values, now I'm in search for the missing link of packing the ...
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### 2D FFT Toeplitz Matrix Indexing

I have a convolution sum_j M(x_i-x_j) v(x_j) which I would like to numerically compute using a FFT. x_i and ...
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### Missing known sinusoid in FFT of sensor data

Let me ask about FFT, i have data sample from sensor, source of frequency from generator is 5 Hz, i want to extract the data with FFT but why i cannot find the 5 Hz frequency from source. This is my ...
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### Is there a FFT algorithm which is both in-place and constant geometry?

I work in crypto where the NTT (Number Theoretical Transform) which is just a FFT in finite fields is used. I wanted to know if there exists an implementation of the FFT which is both in-place and ...
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### DIF based FFT scaling for OFDM Input

I'm working on XILINX FFT IP(PG109) in pipeline mode, which uses radix 2 DIF Lattice to perform FFT/IFFT operation. How to perform scaling of each stage in FFT, such that the effect of saturation or ...
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### How to difference a loud sound (playing notes), from a soft noise in spectrum. (Pitch detection with bass)

I'm trying a program that outputs the bass line that you are playing. I have some arrays from a big one with the sound in time domain, that are splited (Hann window). Later, I do the FFT, then I get ...
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### What is the DFT of a pure cosine wave cos(θ)

I want to find a DFT of a pure cosine wave cos(θ) sampled at N equally spaced points on the interval $[0, 2\pi)$ so for our cosine wave, I put my $x$ like this $x=cos(\phi)$ then I just put it in ...
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### How to get Spectrogram after fft in matlab?

I have many EEG signals which record at 100 Hz. I use FFT on them with fft Matlab toolbox. Now I wanted to get a Spectrogram. As I searched and read a lot, I figure that I should window my signal and ...
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### Signal Timing Recovery, Loop Bandwidth and SNR

As explained in the answer here, for the symbol timing recovery loop we need to keep loop bandwidth sufficiently below the modulation bandwidth of the signal so as to avoid the filtering of the signal ...