The fast Fourier transform is an efficient algorithm to compute the discrete Fourier transform (DFT) and its inverse.
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46 views
frequency domain phase shift
While going through FFT I came to know that, shifting of phase in frequency domain results on shifting of time in time domain.
According to this, in wireless communications, from the transmitter side ...
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2answers
70 views
How to make a signal conjugate symmetric?
Take the simple frequency-domain band-pass filtering operation below . . .
...
3
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3answers
87 views
Basics of frequency spectrum for onset detection using FFT
I'm pretty new on signal processing and I've been reading a lot the last days in order to understand a little about it. But still there are things that I'm not sure if I got well. Sorry if I don't use ...
2
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2answers
55 views
recover image by only magnitude of image fourier transform
I have a image and I want calculate fft2 of it, after it I want recover image only by magnitude of it. how can I achieve this work?
...
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1answer
47 views
MFCC feature extraction
I have a block of audio and I have performed an FFT on it. Now what I want to do is convert this FFT into a set of MFCCs, however while I know I need to do something with weighting the FFT samples ...
3
votes
1answer
101 views
Zero-Padding seems to CHANGE FFT of signal!
I am having trouble with zero-padding. As I understand it, in theory, zero-padding in the time-domain should 'sinc-interpolate' the FFT of the signal in the frequency domain.
This would mean, that ...
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2answers
98 views
Removing noise from audio using Fourier transform in Matlab
I'm trying to remove noise from an audio file. This audio file contains speech as well as constant pink noise. I know that I have to use the Fourier transform to convert to the frequency domain then ...
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2answers
78 views
Frequency array feed real values FFT
EDIT
The first version of my question has not worked as I expected, so that I will try to be a little bit more specific.
The final goal I am trying to achieve is the generation of a ten minutes time ...
7
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4answers
167 views
DFT-like transform using triangle waves instead of sin waves
We know that DFT (discrete Fourier transform) breaks down a signal into multiple frequencies of sine waves. Does there exist a transform that does the same thing, but for triangle waves?
For my ...
4
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2answers
159 views
What is the uHz-rotator algorithm?
According to this page, the Baudline software tool implements
...the uHz-rotator algorithm that operates in the complex domain to
calculate an extremely accurate estimate of the frequency.
...
5
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1answer
114 views
Coloring a waveform with spectral centroid or by other means
Update 5
Some gradient using harmonic series
The color smoothing is ratio-sensitive otherwise it looks bad, will need some adjustment.
Update 4
Rewrote the coloring to happen at source and ...
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1answer
68 views
How do I convert a filter from Spatial to Fourier domain?
I have a small 2D Gaussian image filter that I am currently applying as a window by convolution. I would like to do this in the Fourier domain as a single multiplication. I would like to convert my ...
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0answers
117 views
What are the differences between the various FFT algorithms? [closed]
Wikipedia lists a number of different FFT algorithms:
Cooley–Tukey FFT algorithm, Prime-factor FFT algorithm, Bruun's FFT algorithm, Rader's FFT algorithm, and Bluestein's FFT algorithm
What are the ...
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1answer
50 views
Spatial and temporal frequency of a wave
I've sampled a propagating wave so that I know its amplitude at several equidistant points on a line, and at several points in time. That is, I have this discrete function:
...
1
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1answer
96 views
What do I do with the result of an FFT?
So I am working on a project using digital signal processing, which I am not familiar with at all, and a lot of this is all new to me. I am using SciPy\NumPy to play around with code to understand the ...
5
votes
3answers
119 views
Determining the mean of of a sampled signal (improvements to time averaging method)
I am sampling a signal at 1kHz, which is essentially a single-frequency sinusoid with a DC offset (and a small amount of noise). I don't know the precise frequency of the sinusoid (it is at most ...
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0answers
61 views
How to prevent Signal drifting when changing frequency
When I recreate a signal it seems to look great. But when I try and increase it's frequency (which is done in a for loop and the variable new_freq=2) it starts to drift.
See Image below (The top ...
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2answers
96 views
2D FFT of Vector
I have a bunch of 8x8 images which have been vectorized and formed into a 64xN matrix, X. I'd like to take the 2D-FFT of each of these images without reshaping each column of X into an 8x8 image and ...
4
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2answers
136 views
Optimizing FFT code for 12 bit processing on microcontroller
I want to port the following FFT code on a microcontoller having a very little floating point capability. I want to perform FFT of the output from 12 bit ADC. Since my values are all 12 bit numbers it ...
2
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0answers
55 views
Phase Correlation and Negative Shifts
I am implementing phase correlation algorithm to determine shift between two images.
It generally works, but I am not sure how to interpret the resulting shift.
Pseudocode:
...
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1answer
60 views
retrieving original data from phase and magnitude of Fourier transform
I use this snippet of python code to transform data to Fourier phase and magnitude and then retrieving original data.
...
4
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1answer
69 views
Discrete Fourier Transform a dummy approach
I'm trying to understand how DFT works exactly. However, when experimenting around, I compared both Matlab generated FFT result with a dummy approach result and I get similar result.
However, the ...
3
votes
0answers
83 views
Extra 'fingers' found in graph after applying FFT in MATLAB
I am currently working on the FFT function in MATLAB. In this function, i require a 1024 number of data Time Domain plot and produce a 400 number of data Frequency domain plot.
After applying the FFT ...
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2answers
79 views
Bit reverse order Technique in FFT
Can anyone tell me how does bit reversal order technique works for FFT when you are trying to break down the FFT to small sizes. Like I want to only for the when the index is odd because that involve ...
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1answer
76 views
FFT of size not a power of 2
My question is regarding the input size of a signal which is not a power of 2 and we have to take the fft of it. Some solutions say that suppose if we want to take the fft of 1800 we should zero pad ...
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0answers
39 views
My understanding of finding the solution of fft of size 1536 [closed]
I have already asked this question 2 times, but still i am confused because this is not available anywhere on the internet and explained properly. I found some information in this document and i am ...
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1answer
59 views
Determining sampling rate in OFDM demodulation
I have seen that in OFDM, the sampling rate is much lesser than twice the bandwidth of signal. why is it so? How is sampling rate calculated in OFDM? Does it depend on the modulation type used inside ...
2
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1answer
56 views
2
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3answers
94 views
Effect of windowing on FFT magnitude
I have 2 sin waves:
Fs = 1500;
N = 100;
t = (0:N-1)'/Fs;
sinwave = sin(2*pi*15*t);
sinwaveshifted = sin(2*pi*15*t + 1.3);
If I get the magnitude at 15Hz using ...
3
votes
2answers
91 views
Do I get less accurate results if I do not use a power of 2 points for my FFT?
I heard that the padding with zeros is mainly for efficiency and speed, other than that, is there a downside to use fft(signal) instead of fft(signal, N) where N is a power of 2 assuming signal length ...
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3answers
116 views
Best method to extract phase shift between 2 sinosoids, from data provided
I have been asking around if the way I was extracting phase shift (lag) was correct, and I ran into some trouble... so in general, given 2 arrays of data of the same length, one represents the input ...
1
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2answers
118 views
Solution for FFT size 1536
I have already asked this question 2 times, but still i am confused because this is not available anywhere on the internet and explained properly. I found some information in this document and i am ...
1
vote
3answers
163 views
Am I understanding the phase angle from FFT correctly?
Long story short, I have a sinusoidal wave with DC offset going in with a given frequency of say 100 Hz and $\phi = 0$ (which I'm guessing is really $\pi/2$ since it is a sine wave not cosine). I get ...
1
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2answers
69 views
Ways to analyze electrical signals without FFT?
I am collecting a 15Hz sine wave at 1500Hz. Therefore, every 100 points of data collected should contain a single complete sine wave. If I sample for 10 seconds, I will have 15000 points of data. If ...
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vote
2answers
123 views
FFT for a single frequency
I was looking for a more efficient way of finding the magnitude and phase of a signal at a certain frequency without performing an FFT because it produces more information than I need and I came ...
3
votes
4answers
167 views
FFT of sine wave not coming as expected i.e single point
The cyan plot is a spectrum of 50 Hz, and the magenta one is a 50.1 Hz sine wave (having amplitude 0.7). Both are sampled at 1024 samples/s. I performed a 1024 point FFT to get this spectrum.
Why is ...
3
votes
1answer
96 views
Why can the FFT always be mirrored in the middle of the x axis? [duplicate]
Plotting the FFT of a signal with Matlab e.g. by the code:
y_fft = abs(fft(y));
f = fs*(0:length(y)-1)/length(y);
plot(f,y_fft);
where ...
1
vote
1answer
46 views
Frequency vector and fft
I have got a question concerning the definition of the frequency vector for an fft operation.
Generally, I work with a frequency vector, f, with power of 2 ...
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0answers
33 views
In which bin would the phase angle be in FFT? [duplicate]
Say you have x = sin(2*pi*t*f + phi)
Given, f, t, fs and frequency vector to be f = linspace(-fs/2, fs/2, n);
where ...
3
votes
0answers
67 views
Points of interest in a spectrogram
We have several audio tracks, all of which are different versions of the same track under one type of distortion: the speed of the track is increased by a constant factor K (hence frequences are ...
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3answers
111 views
Finding the dominant tone in a signal
I am given 256 samples at a sampling rate of 48k and am asked to find the frequency of dominate tones and the amplitude of the largest tone. The data looks like this when plotted:
I assume I must ...
2
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0answers
34 views
How to prove that Dilution of a time domain signal results in duplication in Frequncy domain?
While reading a description on FFT from this book, I found the following statement:
...diluting the time domain with zeros corresponds to a duplication of
the frequency spectrum.
How can I ...
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0answers
15 views
Consider filtering n*n images by separable m*m filters.What are the computation time for filtering using FFT;2-D convolution;by two 1-D convolutions
Consider filtering square n*n images by square, separable m*m filters.
a) Give general equations for the computation time for the following approaches to this 1) filtering using FFT 2) by 2-D ...
1
vote
1answer
104 views
How to get fundamental frequency of a signal using autocorrelation?
I am trying to get the fundamental frequency of a signal that only has a single pitch. I coded out the autocorrelation function using FFT and already got the autocorrelation result. Unfortunately, I ...
4
votes
1answer
132 views
What is the phase and magnitude response of white noise?
I would like to create white noise in the frequency domain, and then transform it to the time domain using python. To understand the problem, I simply generated white noise in the time domain, and ...
0
votes
1answer
62 views
Computation time 1) fft, 2) 2-d convolution, 3) two 1-d convolution
Consider filtering square n*n images by square,separable m*m filters. What are the general computation time for the following approaches 1) FFT 2) by 2-D convolution 3) by two 1-D convolutions. ...
1
vote
3answers
83 views
What is the relationship between frequency vector and the peak frequency in FFT?
I am fairly new to both Matlab and FFT. I would like someone to explain to me the relationship between the frequency of the wave being processed, the number of point (usually called NFFT), the Nyquist ...
1
vote
1answer
43 views
Parameter extraction from DFT results, possibly with leakage effects
Let's start with a simple temporal law, that I want to analyze in the frequency domain :
$x(t)=\frac{1}{2}(A+Bcos(2\pi \nu_0 t+\phi_0))$, with :
$A=4$
$B=10$
$\nu_0=10^8$
$\phi_0=10^8$
I made a ...
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1answer
50 views
FFT function isn't working on imported signals greater than a second
I have an fft function in matlab/octave that works great on an imported mono wav/audio signal that is 1 second long, but when the signal imported is more than 1 second the frequency values become ...
3
votes
1answer
35 views
Transform Length and event duration
Does the length of a Fourier Transform affect the ability to discern a small event in the data?
This is a tricky question to ask, let me clarify. I don't care about when the event happened and I ...
