Questions tagged [ifft]
The ifft tag has no usage guidance.
219
questions
0
votes
0answers
29 views
Extrapolation of band-limited frequency data
I'm now studying "How to do accurate transform from band-limited frequency data specifically S-parameter data of high speed interconnect to the causal impulse response in time domain. There are ...
2
votes
1answer
80 views
Hilbert transform in the frequency domain
As I know, the Hilbert transform
$$ H(x(t))=\frac{1}{\pi t}\star x(t) $$
in time domain is equal to
$$ -j \operatorname{sgn}(f) \cdot X(f) $$ in frequency domain. so I tried simple example using ...
0
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0answers
36 views
FFTW audio artifacts when modifying magnitudes in frequency domain
I'm currently working with FFT (FFTW3) that I'm using to apply treatments on audio files frequencies.
The Forward/Backward test is passed, since I can get the exact same soundfile when processing ...
1
vote
0answers
44 views
Sweep synthesis in frequency domain: How to correctly adjust magnitude?
I'm attempting to synthesize a logarithmic sweep signal to measure the IR of a system. For the most part, I'm following Section 5.2 of the paper Transfer Function Measurement with Sweeps.
To generate ...
0
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0answers
14 views
Noise and harmonic elements w/in a discrete time signal
So I have a discrete-time signal with around 300 samples. It is part of an environmental science application, so is not-strictly periodic although there clearly are periodic components. I have applied ...
0
votes
1answer
59 views
Can you use Bartlett method in reverse? [closed]
I'm wanting to do an inverse Fourier transform.
Can I use the Welch method to generate this inverse, by replacing the FT used within with an IFT?
1
vote
0answers
65 views
Implementation of Cepstrum in Python
Actually I want to denoise a signal. I know how can I implement FFT in python to denoise it. This is the implementation which I use(From this Kaggle notebook):
But I don't know :
How can I use ...
0
votes
1answer
171 views
Sparse Inverse Fourier Transforms
I'm looking to compute an IDFT but my input is very sparse:
Example:
IDFT length: 7,408,800 (complex floats)
Sparsity: 96.61% to 99.99%
I found this Sparse FFT website but it looks like the library ...
1
vote
2answers
154 views
Inverse complex FFTW transform
I've been scanning all of the FFTW documentation, trying to figure out how to inverse FFT my FFT spectrum.
The documentation only mentions how to inverse FFT real-to-complex transformations, using the ...
-1
votes
1answer
92 views
Basic upsampling of a signal
I've been learning about the (Fast) Fourier Transform and it's uses.
Using the formula:
$$FFT(concatenate(IFFT(signal), 0^\text{increase}))$$
I was able to go from this signal:
to this:
by settings $...
0
votes
0answers
32 views
Does this FFT algorithm give correct IFFT when the input does not contain symmetry?
This FFT function is from Numerical Recipies in C and I am using it in my java projects. The source code is given below:
...
1
vote
1answer
60 views
calculate fft convolution for an LTI system given its input (in time domain) and its poles and zeros
I have considered taking the fft (MatLab) of the input (x) and create frequency bins for the first half (problems with an odd number of samples, tried solution zero paddings) and evaluate the transfer ...
0
votes
1answer
25 views
how twiddles are calculated in the code snippet below from ti.com?
I am trying to port a C code for fft/ifft to a DSP (TMDSEVM6678LE) from ti.com. In one part of the code it tries to calculate the twiddle coefficients as you can see below; however, I can't understand ...
0
votes
1answer
39 views
Construct IFFT from only the major frequencies of an input signal?
I have data which when plotted looks like the green line in the below image. The data is from the walking-motion of a reinforcement-learning-model in a simulation and therefore the values do not ...
2
votes
0answers
86 views
How to take the inverse FFT of Welch's power spectral density in Python?
I have calculated the power spectral density of a weakly-stationary signal using Welch's method (as implemented by scipy.signal.welch in Python), and am looking to take the inverse Fourier transform ...
2
votes
2answers
2k views
FFT showing peaks at 0Hz?
so I've been attempting to do a FFT on some data and I'm seeing a peak at 0Hz, which I can't really comprehend why since I'm quite new to signal processing. I read in my file using pandas, saved them ...
1
vote
0answers
45 views
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 ...
0
votes
1answer
48 views
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 ...
0
votes
2answers
1k views
Am I supposed to normalize FFT in Python?
I'm sorry if this question is posed often, I can't seem to understand the answers already out there. I'm working with several forms of the Fourier transform, including the FFT, PSD, and spectrograms. ...
1
vote
2answers
104 views
Fourier Transform of sampled reflectance measurements
Goal:
Calculate the complex index of refraction ($\hat n = n +jk)$ from reflectance measurements.
Data:
Reflectance measurements for various materials were taken with a FTIR (Nicolet™ iS50 FTIR, ...
0
votes
1answer
67 views
On the use of Permutation matrix to perform iFFT
I have a question about using the permutation matrix for performing $iFFT$ for such matrix and then reshape it row-wise and column-wise way.
Let's say that we have a random matrix $x$ whose size is (...
1
vote
3answers
113 views
Frequency domain samples to time domain without knowing the sampling rate?
I have some frequency response data from 802.11a OFDM communication in channel 8 of the 5 GHz band, and I would like to inverse transform this to produce the corresponding time domain response. That ...
0
votes
1answer
39 views
Hamming window in frequency domain and back
I can't figure out the scaling and slight artifact in fourth plot.
...
0
votes
3answers
122 views
Windowed N-point FFT
In the previous question,
Smoothing in frequency domain and impulse reponse of the filter in time-domain
I guess I have made a mistake in-terms for applying windowing to FFT.
After reading "...
0
votes
2answers
352 views
Converting PSD to Time Domain Signal
I am currently using MATLAB and I'm thinking if I can reconstruct PSD back to time domain signal using MATLAB's ifft. I found a link in solving this problem but it's in Phyton and when I tried it in ...
0
votes
2answers
55 views
Is there any other method to get the DFT of a signal without actually computing it using normal calculation
Is there any other method to get the DFT of a signal without actually computing it using a normal calculation.
Please help me out in this query
0
votes
0answers
61 views
If you are given an inverse DFT, then how do you convert it back to the DFT without actually computing any DFT?
If you are given an inverse DFT, then how do you convert it back to the DFT without actually computing any DFT?
0
votes
1answer
86 views
Can we use discrete cosine transform with imaginary part
I have been reading about the difference between the use of iFFT and iDCT with OFDM.
What I understood that iDCT can only be used with one phase modulated symbol which is PAM/BPSK modulation.
It ...
0
votes
2answers
223 views
What is Magnitude and Phase actually represents in Fast Fourier Transform?
When we reconstruct the image from its magnitude only using Inverse Fast Fourier Transform, then why the resulting image looks nothing like but the original image? Can someone please explain me in ...
0
votes
1answer
44 views
bandpass waveform detector?
I am hoping that somebody might have a good idea for detecting low-frequency pulses in some rather noisy data (I'm working on improving the snr). I have repurposed a "Raspberry Shake 1D" to record the ...
0
votes
1answer
118 views
MATLAB: Applying Inverse Fast Fourier Transform to an array of real numbers
I'm trying to understand the difference between applying the Discrete Cosine Transform (DCT) and the Inverse Discrete Fourier Transform (IDFT) to the log Mel-filterbank energies as explained in the ...
0
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0answers
176 views
Getting back the original x axis after IFFT-FFT in Python
I have an analitically generated spectrum $I(\omega)$, x axis represents angular frequency, y represents intensity. The spectrum is centered around some frequency value, which is often called central ...
2
votes
2answers
135 views
how I can use the FFT data to compute the convolution?
First,I have a vector A of length N,through process
...
0
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0answers
153 views
Stolt interpolation and ifft in range migration algorithm
I am using range migration algorithm for focusing stripmap synthetic aperture radar data. I have successfully tested my algorithm using the following steps after range compression (similar to this ...
0
votes
0answers
17 views
What is the correct input format to perform IFFT on a spectrum?
Say I have response of a band pass $\left(f_1-f_2\right)$ or a lowpass filter $\left(0-f\right)$ and if I want to estimate filter length then I may take the inverse transform of the frequency response ...
0
votes
0answers
44 views
How to applly Hanning window on S parameter results?
I am working on Time domain computation. I have S parameter results simulated, using these results I do the Inverse FFT to get results in time domain.
I want to filter/window results using Hanning ...
0
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0answers
61 views
Cepstrum calculation with 5-smoothing zero padding
I am trying to compute cepstrum of a signal x
An implementation of this in python is:
...
0
votes
1answer
266 views
FFT of square wave: maths and actual numbers do not coincide
this fact is driving me insane... Theory states that the Fourier transform of a square wave is a sinc function, but if I compute the fft of a synthetic (perfect) square wave of amplitude 1 and ...
0
votes
2answers
213 views
What is the meaning of the length of diagonal lines in FFT
I am relatively new to FFT analysis of images and have a question about them. I like to think I understand the basics but many of the properties shown in a FFT image are beyond me.
My main question ...
2
votes
0answers
114 views
White noise generation in frequency domain (stfft) produces a periodic pattern
I have created a set of spectral processing modules for SynthEdit next to be released, implenting short time fft, so I am now quite experienced with the matter, but recently encounteted an unexpected ...
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0answers
97 views
Scaling issue after doing manipulations in FFT
I have two filters which must apply (in series) to same input data $x[n]$ e.g of length 256 (real time asio input buffers). One filter is e.g. an impulse response $h_1[n]$ of a speaker and other one ...
0
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1answer
56 views
0
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1answer
114 views
IFFT of a complex, conjugate-symmetric transfer function - Value at Nyquist frequency
Using the MATLAB 'symmetric' flag to compute the IFFT of a complex-valued, length-N (with N even), transfer function, the imaginary part of the complex value at the index ((N/2)+1) corresponding to ...
1
vote
3answers
134 views
fft and inverse fft error size and applying impulse response matlab
I have a signal called noise. I am using the following command to calculate the mean squared error after fft and inverse fft process:
...
0
votes
1answer
65 views
What happens if I zero out the initial terms of the fft output and take inverse fft? [duplicate]
I am new to signal processing domain. When I run fft on data of length 1000, I get 1000 complex numbers. Now, if I want to extract the low frequency information or signal approximation, I take the ...
0
votes
2answers
1k views
inverse discrete fourier transform with plain python
I am trying to calculate inverse discrete fourier transform for an array of signals.
I am using the following formula:
$$ x[n] = \tfrac1N \sum\limits_{k=0}^{N-1} X[k] \, e^{j 2 \pi k n/N} $$
And my ...
2
votes
1answer
69 views
What is the proper way to filter out unwanted noise from accelerometers?
I'm a beginner in signal processing and have a hard time to filter out environmental noise from the floor vibration data collected using accelerometers.
I have tried using butterworth filter (IIR) ...
0
votes
2answers
186 views
My impulse response does not tend to zero
I am doing an IFFT of frequency response data achieved with Simulation tools.
When I plot my impulse response it looks wrong as the response does not tend to zero as it should. Instead there seems ...
0
votes
1answer
180 views
Inverse FFT of complex exponential with time delay - window leakage?
I am working in MATLAB with a frequency domain signal that is a sum of complex exponentials, e.g.
$X(\omega) = \sum_i e^{-j\omega t_i} $ where $t_i > 0$ $ \forall $ $ i $
I expect the output to ...
2
votes
0answers
97 views
Correct way of derivating in frequency domain with FFT
I believe I am very close to the answer and only need a small nudge to get to the answer.
What I want:
I want to take a signal, use FFT to transform it to the frequency domain (FD), multiply it by $...
