New answers tagged fft
0
votes
Inverse fft does not give back the same image
Then obviously the function doesnt use the identity kernel for the convolution.You can write your own code to do the convolution by using the identity kernel.
- 23
0
votes
what degree of accuracy does quadratic interpolation add to fft cross-correlation?
There should be plenty of literature out there on the accuracy of TDOA methods. An example is
S. Stein, "Algorithms for Ambiguity Function Processing." IEEE Transactions on Acoustics, Speach,...
- 844
4
votes
Accepted
Inverse fft does not give back the same image
When you use imread() on the image, the output is array of uint8.
When you apply the fft2() ...
- 19k
1
vote
Help on audio filter with FFT on python
I've heard that some sounds in most languages use some very high and low pitched frequencies, so it would make sense it doesn't sound complete after those frequencies are removed. Getting rid of the ...
- 11
2
votes
Accepted
Converting cutoff_frequency_ratio to Cycles/Pixel in Butterworth Filtering with skimage
How can I convert cutoff_frequency_ratio to "cycles per pixel"?
They are the same thing. By expressing the cut off in terms of the ratio, the physical units, whether they were samples per ...
- 844
1
vote
Is there an a method to fit a wave created from two wave?
I am not an expert on FFT and numerical modeling. I just tried to make an attempt since no one is answering the question. I used trial and error and gets an okay fit. I do not understand why I need to ...
- 11
2
votes
Why will the output be imprinted with delay effect or echo after convolving two direct dry signals' FFT values (convolution filtering)
The correct way of doing this is overlap add. Neither version of your code looks remotely like a correct overlap add implementation, so chances both are wrong.
The proper way to determine this is to ...
- 41.4k
2
votes
Why will the output be imprinted with delay effect or echo after convolving two direct dry signals' FFT values (convolution filtering)
The difference in the behavior of the two methods, particularly the delay or echo effect in the first method, is primarily due to the way the kernel is being used in both methods.
In your first method,...
- 1,131
2
votes
second harmonic dominant effect, why does it happen?
Either the values in the harmonics plot are the harmonics of the waveform different from what you show in the signal plot, or, because of the calculating/plotting inconsistency, the frequency axis in ...
- 1,589
2
votes
Accepted
second harmonic dominant effect, why does it happen?
mathematical interpretation of the harmonics.
That is easy enough: Any function that's periodic with $T$, i.e. $x(t) = x(t + kT), k \in \mathbb{Z}$ can be represented as a sum of sine/cosines, i.e.
$$...
- 41.4k
1
vote
How to rebin FFT results
The increased bin size corresponds to a decreased total duration in time for the equivalent time domain waveform.
If a complex valued FFT is desired (accurately representing the magnitude and phase as ...
- 48.2k
1
vote
Accepted
Extracting the phase using FFT without detrending
Is it possible to get the π/4 phase using FFT without detrending the signal?
Not really. You have the sum of two signals: the drift and the sinusoid, i.e.
$$x[n] = M\cdot n + A \cdot \sin(\omega n + \...
- 41.4k
2
votes
Uncertainty error in phase and amplitude results of FFT MATLAB
The DFT (Discrete Fourier Transform) is a linear operation, so if you have a signal $x[n]$ with some additive noise $q[n]$ we have
$$y[n] = x[n] + q[n] \\
Y[k] = X[k] + Q[k] $$
where $X[k]$ is the DFT ...
- 41.4k
0
votes
Uncertainty error in phase and amplitude results of FFT MATLAB
The uncertainty in the calculated spectral amplitudes will be related to the uncertainty in the measured time-domain signal amplitudes, the uncertainty in the time measurement, and also the sampling ...
2
votes
Accepted
How to get x-axis when using FFT to cross-correlate
Let's say we have two discrete functions $f[n]$ and $g[n]$ that have finite support on $[m_f, M_f]\ m_f,M_f \in \mathbb{Z}$ and $[m_g, M_g] \ m_g,M_g \in \mathbb{Z}$. Than the lengths of the ...
- 41.4k
1
vote
Accepted
N-point DFT of window function
So, can I assume that the 2n-point fft is more accurate than the n-point fft?
No. The N-point FFT contains all independent information that is required to completely represent the spectrum.
And how ...
- 41.4k
0
votes
fast fourier transform band pass filter only on positive frequency
The only positive frequencies came from the construction of the analytic signal. If we have a real signal (with positive and negative frequencies in its spectrum) $s(t)$ we can construct its analytic ...
- 71
5
votes
Accepted
removing spikes from spectrum
These spikes look like harmonics of some sort of line noise at $250 \texttt{MHz}$. To get rid of these, what you need is a comb notch filter.
There are a few ways to build one.
If the fundamental (...
- 4,784
0
votes
Simulating analog filter using convolution or converting with fft
I need something similar in Python but I can't understand what's wrong...
creating simple 1th order low-pass Butterworth filter, Fc=10Hz
# creating I order, 10 Hz, low pass Butterworth filter
fc = ...
- 1
1
vote
How to do FFT with complex numbers - Ansi C code
Up until a few years ago, MS Visual Studio supported C only as C89. Which was a major pain in bigger projects locked into that IDE/compiler and multi-platform projects.
If possible, I would use a ...
- 3,270
2
votes
How to do FFT with complex numbers - Ansi C code
Radix-2 FFT written in ANSI C. This is really ducking old.
...
- 19.8k
Top 50 recent answers are included