# Questions tagged [ifft]

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### FFT filtering by hand in python - iffy issue - cannot get filtering right

I am trying to filter an image by hand (with no using the image processing libraries) to understand how fft.shift works in python. No luck. I take a png an image from MNIST, e.g.. Here is the code: <...
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### Properties of the Frequency Domain to Ensure a Periodic Inverse Discrete Fourier Transform

I've been working on a project to send data via sound waves. The way I've carried this out is by encoding the data in pulses in the frequency domain, and then creating a unique sound wave containing ...
49 views

### excluding the value of some frequency in a Fourier Transform

I have a variable in time and I calculated its mean which is 9.5. I have done the Fourier Transform of this variable, using the FFT in matlab. I would like to consider only a range of frequencies, so ...
40 views

### Change spectrum and normalization

I have a question about magnitude of a spectrum. My task is to build the spectrum and make IFFT - the result waveform should have unity amplitude. For example: Create 2 arrays with Magnitudes and ...
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### OFDM IFFT/FFT processing

After the serial-to-parallel to break input bitstream into groupings we do the constellation mapping into values of phase/amplitude (or I, Q). For 64 sub-carriers this gives us 64 pairs of amplitude(n)...
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### 1ppm Sampling clock offset in Matlab

How to emulate a sampling clock offset (between the transmitter and the receiver) of 1 part per million (SCO=1ppm) in Matlab? Theoretically, I can upsample the signal by a factor of 1,000,001 (one ...
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### implmentation of FFT using lower N point

I have random data which was generated using randi funtion of 1024 bits.. I will modulate this using QPSK and will pass through 512 point IFFT.. While doing reverse process, I want to use 256 point ...
39 views

### filtering large wiggles in signals

I am trying to filter out large wiggles showing in a signal. Those wiggles are happening due to many signal processing layers and a final sine Fourier transform (no phase) Here's the python code i am ...
59 views

### How an algorithm for measuring the analytic signal (Hilbert transform) gives us complex value at the end?

I have a question about the following codes for measuring analytic signal (Hilbert transform). Here,the time domain signal (x) is a real value signal. After making fft it becomes complex (X). Then it ...
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### How to multiply two FFTs in MATLAB?

I want to find the output signal(y) from input signal(x) and impulse response(h). To do that first I take the fft of both x and h, then multiply them, and finally taking the ifft of the result. The ...
76 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 ...
47 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 ...
277 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 ...
30 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.
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### 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 ...
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### 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 ...
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### 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 ...
57 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 ...
195 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 ...
173 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 ...
82 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 ...
176 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. ...
38 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 ...
259 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 ...
106 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 ...
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### 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 ...
63 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?
188 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 ...
224 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 ...
455 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 ...
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### 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 ...
61 views

### Hamming window in frequency domain and back

I can't figure out the scaling and slight artifact in fourth plot. ...
164 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 "...
1k 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 ...