Questions tagged [ifft]
The ifft tag has no usage guidance.
231
questions
0
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2answers
44 views
Convolution Reverb Calculation
Here's my basic understanding of how to implement a convolution reverb:
I measure the IR of a space using a sine sweep. The raw mic output is stored as a Voltage-Time data set. Let's assume that this ...
0
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1answer
28 views
How to do sliding window multiplication in frequency domain
I want to perform the following computations with the impulse response of length L of a LTI system:
Multiply the impulse response with a window w(n) of length M << L.
Take the FFT of the result ...
0
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1answer
47 views
What is imaginary part after IFFT and how to use it?
let's say we have signal in time domain.
After we make FFT on it we will receive that signal in frequency domain.
And as far as I know the real numbers mean magnitudes of each frequency bin, and ...
0
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1answer
21 views
Spectral efficiency of with OFDM vs without OFDM?
OFDM has advantage over frequency selective channel with addition of cyclic prefix after IFFT of MPSK or MQAM symbol. but I wonder that the spectral efficiency of with OFDM vs without OFDM.
0
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1answer
28 views
does ifft of higher order equal upsampling signal
I have a signal with length 2000, and am taking an fft by 2048, after I perform analysis and some operation on signal in frequency domain I tried to convert it back to time domain. I received a signal ...
1
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1answer
39 views
How do you map indices to twiddle factors in FFT
I am kinda lost on how to map my indices for each stage to my look up array of precomputed twiddle factors.
For an $N=8$ point FFT i have $N/2$ twiddle factors in total:
${
[0] = W_8^0, [1] = W_8^1, [...
0
votes
2answers
57 views
Understanding the twiddle factors
So I've been looking at this butterfly diagram to try to understand it better:
And I am trying to get a good understanding of the twiddle factors.
The definition is given as:
FFT Twiddle Factor: ${e^{...
1
vote
3answers
187 views
Polyphase filter bank channelizer FFT or IFFT
I am referring to the Xilinx application note Polyphase Filter Bank Channelizer. The receiver portion should have FFT but the pdf mentions IFFT in both Tx and Rx.
The paper by F. J. Harris, C. Dick ...
0
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0answers
14 views
How do I perform 2D Fourier domain multiplication if the filter mask doesn't match the image size?
Let's say I have an image that is 512 x 512 pixels. I've been tasked with creating two ideal half-band low-pass filters that will filter the image. The first filter is 8 x 8, and the second one is 16 ...
0
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1answer
34 views
What is the algorithm to generate sine waves of arbitrary frequency in the STFT domain?
I'd like to write a DSP algorithm to do additive synthesis using arbitrary sine waves with inverse rectangular FFTs.
This requires two things:
The ability to generate phase/amplitude lists that cause ...
0
votes
1answer
97 views
FFT on a Raspberry Pi
I'm trying to determine the processing time required to perform a FFT of length 500,000 on a Raspberry Pi in C/C++. I have had difficulty finding any information that would be useful for determining ...
3
votes
1answer
141 views
Circular Convolution and FFT of power 2
I am currently trying to understand the Chirp Z Transform, and compute an FFT for a vector that has size which is not necessarily a power of 2. The key step in the Chirp Z transform to recognize that ...
0
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1answer
49 views
Generating a time domain signal using the fundamental frequencies
I currently have the power spectrum (in dB) of a signal through which I obtained the fundamental frequencies and amplitudes. My question is: how to generate a time domain signal using these amplitudes ...
0
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1answer
98 views
Swift vDSP rFFT not same as Python np.fft.rfft()
I am trying to implement real FFT in iOS, for that i am using Accelerate Framework. Here is my Code for Swift.
...
0
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0answers
35 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
180 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
65 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
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0answers
60 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
16 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
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1answer
60 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
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0answers
124 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 ...
1
vote
1answer
197 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
276 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
118 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
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1answer
94 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
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1answer
32 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
57 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
321 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
3k 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
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1answer
59 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 ...
1
vote
2answers
3k 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
117 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
75 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
149 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
52 views
Hamming window in frequency domain and back
I can't figure out the scaling and slight artifact in fourth plot.
...
0
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3answers
138 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
670 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
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2answers
66 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
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0answers
63 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
111 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
706 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
45 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
192 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 ...
2
votes
2answers
146 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
264 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
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0answers
52 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
107 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
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1answer
358 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 ...
