# 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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### Guitar Tuner or Guitar effects Algorithms? [closed]

I need to explore the algorithm of the digital guitar tuner or the digital guitar effects algorithms. Is there any Book or articles that you recommend of? All I know is that relate to DSP. thanks
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### Preparations to implement FFT on a wav file (code Java, not Library)

I am making preparations to implement FFT on a wav File.wav Only Java. I'm reluctant to use matlab I have a File wav stereo, 16 bits. I need to calculate the FFT, but I have confusing. My File has ...
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### How to process video with DFT/FFT - getting the frequency of green color changes?

Goal: I have a video stream from a webcam. I need get frequency of the green color changes on the video. Video color space is RGB The signal looks sinusoidal with a frequency range 0.5 - 2.4 Hz I ...
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### Implementing FFT in Matlab

I am facing a trouble implementing the fft and appreciate your advice. My data structured as follow: The data are retrieved from the share market for one day change in the share price. The time range ...
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### what I'll get if I take FFT of a frequency domain data

What I'll get if I take FFT of a frequency domain data. I have two questions related to this. For ex, x is a time domain data where X = fft(x), now fft(X)= what i'll get ? While reading SCFDMA, data ...
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### Algorithms for computing FFT in parallel

I am trying to parallelize the computation of an FFT on terabyte-sized signal files. Right now such an FFT using an open-source library takes many hours, even running through CUDA on the fastest GPU I ...
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### defining the frequency range with fast fourier transform

In the following example I have used various examples found on the web to understand fft and detecting signals with matlab. ...
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### Algorithm to find spike

I've been doing FFT's (on sound) for a while and usually use the highest intensity or the ones above average to get the spikes in an FFT result. What would be a good method to get all the 'spikes' in ...
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### Matlab: Estimating power spectral density of an experimental data?

How do I estimate PSD in matlab ? There are lots of methods to estimate, depending on application. I am using an experimental data to identify faults ( e.g. interturn fault of electric motor), which ...
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### How to do smoothing without affecting phase

I have signals captured from two channels of a measurement system. There is phase and magnitude differences between these two signals. I want to apply nonlinear smoothing to the magnitude, but the ...
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### spectral division

Sorry if this is elementary. If I add a small sinusoidal signal to my data and then take FFT of both my original and the modified one and then inverse FFT the division of the two, I should then be ...
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### Advantages and disadvantages of Hilbert-Huang Transform versus Fast Fourier Transform? [closed]

Which one is better for frequency detection? In what circumstances? Advantages and disadvantages of both? Which would be better for a Voice Activation Detection algorithm? Which would be better for an ...
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### Time domain interpolation using FFT with zero padding on the end

I've got a situation where I'd like to use an FFT to do interpolation in time on some complex data (I need to go to the frequency domain anyways to window my data). The notional way of doing this ...
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### Gammatone filter vs 2D FFT for spectograms

I am working on speech segeration and each source I am reading , spectograms are being made by filterbanks which uses gammatone filters . I can't find a proper c++ source code which would make me ...
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### Understanding FFT bin resolution

For a signal sampled at $f_s$, the frequency resolution (or "bin width") for an $N$ point FFT is $f_s/N$. Does this mean that the $k$th bin will contain energy from sinusoids within $0.5f_s/N$ on ...
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### Phase of the FFT of a sine function

I'm trying to wrap my mind about what happens in Matlab/Octave when you compute the fft of a sine function. Theoretically, the Fourier Transform of a sine is given by two delta functions multiplied by ...
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### Does convolution done via the FFT _undo_ computational gains when signal has zeros every other sample?

Suppose we have filter $h[n]$, length $N$. If I use it to do convolution in the time domain, then there will be $N$ multiplications each time during the sliding. (Ignore border conditions for now). ...
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### Add harmonics to a FFT decomposed signal

i would like to add even harmonics from the data of FFT of a signal. How do i do that ? do i have to search for higher magnitude frequencies then add the $2f$ then $4f$ etc ? I understand how to do ...
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### Can you quarter the processing time for real, symmetric FFTs?

The DFT of a real signal is Hermite-symmetric, so you can roughly halve the computation time/memory by not bothering to calculate half the values of the spectrum (and complex conjugating the existing ...
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### Why use a gaussian low pass filter, when we can convolve with gaussian kernel

Sorry if this question is too simplistic, but I am new to image processing and after successfully writing two programs, a convolution program and a low pass filtering program, I noticed that for ...
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### DFT and then IDFT does not provide the same signal

I'm new at Fourier Transforms. I'm using AForge.Math FFT/DFT algorithm (C#). Said that I have this situation: My signal: $$1.4 + sin(2\pi t) + 0.4sin(5·2\pi t)$$ Sampling: 100 samples each second....
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### Averaging frequency spectra gives incorrect RMS

I am averaging several FFT results together in an attempt to get the average frequency spectrum of a track of audio. I'm attempting to use Parseval's Relation to get the RMS of the audio from the ...
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### Using FFT to extract a specific frequency range in Matlab?

I have a signal and from that I want to extract a specific frequency range, e.g. 10Hz to 15Hz. Now I heard that I should use Fast Fourier Transformation. I'm going to do that in Matlab, but I have ...
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### Image processing free open source libraries

This is the first time that I post a question here so excuse me for asking such a beginner question. what free open source <...
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### Is there any problem with my FFT method?

I am trying to analysis a system by Fourier Transform. my system has 3 dominant modes. (1,0.05) (0.51,0.01),(0.46,0.01) the pairs are defined as (freq,damping_ratio) I've got those result with ...
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### FFT frequency domain averaging and zero padding

I'm trying to get the average frequency response of an entire piece of audio by splitting it into segments, doing an FFT on each one, and averaging the magnitudes together. Its working great until I ...
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### Why does an fftshift in the time domain give a different result compared to the frequency domain?

I am trying to speed up some of my code and for physical reasons I need to do an FFT shift to get the FFT data in the standard DFT fourier representation. In Matlab this is performed in the frequency ...
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### Algorithm to zero pad data before FFT

I've seen some other questions on here about zero padding (like this one) but I'm still a little confused about my situation. I'm attempting to zero pad my input time series data, so I get an ...
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### how to plot amplitude and phase of IMDs from their fft values?

i have my output as vector of 60000 complex number representing 10 sequence in frequency domain , each of length 6000. i need to plot the phase and amplitude of intermodulation distortion from this ...
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### FFT and aliasing

I have got a txt file which contains voltage and time data. When I did fourier transform using fft function in matlab I got complex numbers. I understand that the real part is the magnitude and the ...
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### Estimating the wavelength of a sinusoid

I have a sinusoidal signal embedded in noise, and I would like to estimate it's amplitude and frequency, so I can subtract it out. I realize that an FFT can do the job for me, and that's what I've ...
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### Revert anayltic signal(length(N/2)) to real signal (length(N))

As a beginner in signal processing, i'll try to explain my problem most thoroughly. I'll firstly explain the idea of the transformation the real valued data has undergone. This includes the ideas and ...
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### Similarity in absolute value of nearby DFT coefficients

Is there any approximate relation in FFT coefficients? For example, consider time domain signal $x_n$. Its $N$ point (assume $N$ to be even) DFT is given as $X_0,X_1,...,X_{N-1}$ Can I say something ...
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### How to calculate the similarity of two electric waves

I have two electric signals from different sources and I think that are similar. I have the FFT of the signals and I have their spectrums of frequency in separate arrays. How should I proceed to ...
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### Missing harmonics (power-line)

I have some biomedical signals. If I calculate their magnitude spectrums, I see power-line interference at 50 Hz. I was excepting a harmonic at 100 Hz, but it turns out there is none. However, there ...
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### Low pass filter with DFT

This is my first question at this site, please excuse me if I'm not asking the question properly. I have an acoustic signal of a test and I want to remove the "thin" peaks, because they don't really ...
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### Isolating Bat Species without prior training base

I am attempting a project and I have been given Bat calls (in .wav) which are not ultra-sound navigation calls and I'm looking to isolate the different species of bats and monitor their activity. ...
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### Units of FFT frequency

I'm having some trouble understanding FFT plots and measures. According to this, this will give me the magnitude plot of FFT, ...
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### Given an experimental FFT plot, how to find the best match from a set of generated FFT plots?

What I'm trying to do is, given some experimental data and it's (magnitude normalized to 1) FFT, match the FFT with one of say 1000 other (magnitude normalized to 1) FFT plots. Please note that the ...
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### When should I calculate PSD instead of plain FFT magnitude spectrum?

I have a thirty-second speech signal that was sampled at 44.1 kHz. Now, I would like to show what frequencies the speech has. However, I'm not sure what would be the best way to do that. It seems ...
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### Offset effect in FFT magnitude

i will use matlab code just for convenience, i get the same behavior using a C++ code. I have two signals: ...
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### 1/n octave smoothing

Given a frequency response obtained with FFT, I would like to apply a 1/n octave smoothing. What filter should I be using and how? Maybe someone could point to a good reference (a paper or book on the ...
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Let's say I have two images that are parts of the same bigger image, cut using two masks (for simplicity, let's assume that the masks are just rectangles of the same size). The images are presumed to ...
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### Complex Cepstral Transform and Audio Watermarking

I am doing research in audio watermarking and have come across the paper that uses the complex transform to embed the watermark in order to improve the robustness and inaudibility of the embedded ...