Questions tagged [ifft]

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1answer
771 views

Inverse Fast Fourier with overlap

I had to work with sound(denoising algorithms), when I read about an algorithm it said that we do DTSTFT(Discrete-time short-time fourier transform) we will create an overlap between each "chunk" of ...
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1answer
273 views

taking FFT from DCT

There is a speech signal, $y[n]$, in the time-domain. To take it to the frequency-domain, DCT has been got from $y[n]$ (w = dct(y) in MATLAB). After it, I applied ...
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1answer
1k views

How does MATLAB recover picture from magnitude spectrum alone?

This is the transformation I did. The code fft2() the Lena picture than ifft2() it back to the original. Add some ...
3
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2answers
475 views

What is the effect of the natural logarithm in the frequency domain?

I have read that taking the natural logarithm of a signal $x$ in the time domain will introduce a spectral broadening and hence "up-sampling" process before the logarithm is required. I tried to test ...
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0answers
897 views

Vibration Acceleration Analysis with FFT and inverse FFT

I've been reading time series data off of an accelerometer, and converting it to one RMS acceleration in g. The sensor works in a range of 0-6.4 kHz approximately. Ideally i would like to restrict the ...
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1answer
432 views

Efficient computation of inverse FFT of real sequence using half sized FFT or inverse FFT

The inverse FFT of a folded real sequence yields a real symmetric sequence. Are there any ways to exploit this symmetry to perform a smaller complex FFT or complex inverse FFT? Background: it's ...
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2answers
849 views

Signal reconstructed using IFFT: amplitude scale larger than input

I am trying to test reconstruction of signal from IFFT. Below is the python program. I break the signal into overlapping windows and do FFT after multiplication with window function. Then I apply IFFT ...
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1answer
674 views

Bit-reversal equivalence on IFFT (radix-2 Cooley-Tukey)

From everything that I read on the internet, I understood that when performing FFT or IFFT, one should perform bit-reversal to obtain a result in natural order (Assuming input is also in natural order)...
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1answer
2k views

Inverse Fourier transform - porting from MATLAB to Python

I am porting a script from MATLAB to Python, but I am failing when it comes to the inverse Fourier transform. The function in MATLAB (ifft) includes a 'symflag', which treats the data as conjugate ...
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1answer
2k views

How to perform 2D image rotation by FFT based image translation using matlab?

I am studying rotation using 3 translations as described in this scientific paper. According to the authors , it is possible to decompose a rotation into 3 shear translations which will be implemented ...
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0answers
182 views

Down sampling in the frequency domain

I would like to down sample a signal from it's original sampling rate of 2,000,000 samples per second to 48,000 (or 44100) starting from the output of an FFT. This FFT delivers 16384 data points (...
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1answer
2k views

Upsampling and Downsampling using IFFT and FFT

Assume in OFDM , there are N=64 subcarriers. I would like to upsample my signal by Factor 8 after IFFT and pass it through channel then downsample it by factor 8 before FFT. I can use upsample, ...
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1answer
424 views

Implementing OFDM with audio signals

I've read an interesting paper called FingerIO that transmits audio waves in OFDM, and I wanted to implement and generate sounds using MATLAB. (I am quite new to signal processing, so please ...
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1answer
2k views

Implementing Frequency Domain Convolution in MATLAB (Convolution Theorem)

I'm trying to prove convolution in time domain is same as multiplication in frequency domain but I'm not getting the same answer in matlab. Here is the code:
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2answers
41 views

Why there is no $dxdy$ and $\Delta k_x \Delta k_y$ in MATLAB's $\tt fft2()$ & $\tt ifft2()$ functions?

In analytical 2D Fourier Transform, integrand is multiplied by $dxdy$. In algorithm of MATLAB function fft2(), this is not done. In discrete case, $\Delta x = Lx/...
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0answers
584 views

Symmetry and mirror of inverse FFT

I am trying to do an inverse FFT to get the real signal from a derived formula which describes the Fourier transformed signal. I am doing this with FFT. I am fairly new to the theory of FFTs, so my ...
3
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1answer
692 views

Spectral centroid manipulations

So, I've created a simple sound analysis application and one of the features I've implemented is the spectral centroid (as explained here https://en.wikipedia.org/wiki/Spectral_centroid). In order to ...
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0answers
55 views

Increase power for particular frequencies

I am taking an FFT of two signals ( A very clean signal, with little noise, and a very noisy signal). Signal A The signal that has very little noise has the following FFT output: Signal B The ...
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2answers
380 views

Problem getting IFFT to work

I've run into an issue fiddling with the FFT/IFFT routines given here (http://www.dspguide.com/ch12/3.htm). I've rewritten the code to C++ and played with it. The idea is to read a raw wave file (...
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1answer
129 views

Subtracting signals to re-construct the middle

Below image represents a sample of some of my captured data. There are three waves if you will. The middle wave has a very large dip ( cluttered by noise ) . My goal here is to try and resurrect the ...
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2answers
135 views

Controlling a signals amplitude in the frequency domain [closed]

I want to control the amplitude of a signal I'm creating from a user drawn spectrum by scaling the magnitude values in the frequency domain. Here is my scenario. Sample rate $F_s= 44100\textrm{ Hz}$...
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1answer
1k views

Overlap and windowing a signal for signal processing

I’d like to digitally signal process an audio data. Therefore my idea was to: Split the audio data into individual blocks of 16 samples each. Each block has an overlap of 50% (8 samples are shared ...
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2answers
578 views

FFT and IFFT : filtering frequencies

I am sampling at $30 Hz$. I have a sample of $N=150$. Here is an example of how my sample looks like, which starts at 54 and ends on 203 on the X Axis I am interested in observing frequencies ...
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1answer
400 views

Uncovering data from noise

I've recently started experimenting with DSP, specifically, understanding digital signals that are generated by some small applications I am creating. For this quest, I've decided to use The Scientist ...
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1answer
401 views

How the increasing of sampling frequency in OFDM didn't cause increase on the required channel bandwidth

In OFDM, how the increasing of sampling frequency didn't cause increase on the required channel bandwidth (fs>>BW), as i know sampling frequency means number of samples per second, if this number of ...
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1answer
110 views

MATLAB: Fourier transform vs $\tt lsim$, results don't match

My (simplified) problem: Suppose I have a signal $u$, which passes through system/filter $G$, which gives output signal $y$. Then I have a theorem that states: If a signal $u(t)$, with Fourier ...
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1answer
639 views

frequency domain zero padding in OFDM

I have a matlab code for OFDM system, in this code the auther added a zero padded subcarriers before the IFFT stage, in the middle of the raws, and added zero padded guard interval after IFFT, my ...
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1answer
188 views

IIR filtering vs IFFT filtering by zero binning and making bandpass IIR filters with high sample rates?

I am having some issues making thin IIR filters that work at the sample rate of my data and was wondering if there is a way to improve my method? I am also curious about the deficiencies in using the ...
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1answer
409 views

How to get a real signal back to a non-complex form after processing it in frequency domain (using fft)

I have an audio signal that is composed of 2 channels. The signal is all real numbers. I transform this signal into frequency domain using fft, multiply it with a filter frequency response, and then ...
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1answer
470 views

ifft doesn't recreate original signal

I want to convert given signal into frequency domain and do some calculation and then convert that signal into time domain. Here is the code which I am trying out ...
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1answer
326 views

How to explain IDFT of square root of a DFT?

I have this MATLAB code: w = [1 2 3 2 1]; W=fft(w); V=sqrt(W); v=ifft(V); And I need to explain how to get to $v[n]$ without using the direct formula for DFT - I ...
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1answer
455 views

Frequency bin of the positive and negative frequency

I am using this MATLAB tutorial for Frequency-Domain Linear Regression. There is one part of code they provide, where it is necessary to determine the "frequency bin of the positive and negative ...
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2answers
2k views

Calculate IFFT using only FFT? [duplicate]

Say you start out with $A=\left\{3,−1,0,0\right\}$, run fft() and end up with $B=\left\{2,3+j,4,3-j\right\}$. What specific steps would need to be done to obtain $...
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2answers
5k views

Implementing inverse FFT using forward FFT

I am trying to implement an inverse FFT using the forward FFT. For clarity: Let S[t] be a signal in time, and S[w] the transformed signal. As per this site, it seems one can reverse S[w], use the ...
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0answers
199 views

How to iplement fast DCT-III (for inverse of DCT-II) using FFT or iFFT

I have to implement DCT-II and its inverse which is equivalently given by a forward DCT-III. All from real to real. I have been checking some paper where it is specified how to do it. However, I ...
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1answer
269 views

How to find correlation between 3 signals

I have 3 signals, S1 S2 S3, with a same time domain and same time steps. I'm wondering if there is any correlation between these 3 signals. more specifically I want to know if it is possible to make ...
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1answer
8k views

Delete frequency components with FFT and IFFT [duplicate]

I have a signal in Matlab defined by signal and t. As it is a noisy signal, I want to delete every component below a certain ...
2
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3answers
1k views

How do you save/convert an image to be in the frequency domain?

Quick Note: I don't believe this is a subjective question... however if it is I will gladly modify to be more objective In ImageJ, if I take the FFT of an image, how can I save this new frequency ...
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2answers
625 views

signal analysis and synthesis with different window length and FFT length

I'm coding an analysis/synthesis system on MATLAB. I was able to recover the original signal when the length of the window (winLen) is set equal to the length of ...
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1answer
1k views

Filter - Spatial Domain Versus Frequency Domain

Note: This is a followup question of How can I create a custom band-pass filter?. Can you explain the following python source code?. Bandpass filter bank. Suppose, I have an equation ...
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1answer
266 views

Confused about DFT symmetric behavior for real-valued signals?

I have a simple and might be a preliminary question about symmetric property of DFT of real valued signals. From definition we know, DFT coefficients of a real-valued signal is conjugate symmetric, so ...
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2answers
793 views

What would be the outcome of the convolution of two images? [closed]

Lena Mask I have written a C# code which produces the following output. Is my output correct? Am I padding in the correct way?
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1answer
93 views

Is it possible to Denormalize a matrix of complex numbers?

In this article, FFT and I-FFT are achieved as the following: FFT steps process starts with a Bitmap image. Bitmap-image to Integer-image Integer-image to Complex-image Apply Forward-FFT to Complex-...
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4answers
9k views

Is it possible to apply inverse Fourier transform (I-FFT) to the following image?

Suppose, I have this image in my hand and nothing else. Clearly, this is a Magnitude-plot of some unknown image. Is it possible to apply an Inverse Fast Fourier Transform (I-FFT) operation to recover ...
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1answer
3k views

Cross-correlation and auto-correlation of an image using $\tt fft$

I'm working on a project where I have to find the auto-correlation and cross- correlation of types of pixels in an image: I am using MATLAB and my code for the autocorrelation is: ...
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3answers
2k views

MATLAB: $\tt fft$ and $\tt ifft$ scaling

In MATLAB, the outputs of the fft and/or ifft functions often require additional processing before being considered for analysis....
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1answer
4k views

Difference between frequency sampling and windowing method

These two filter design methods seem fairly similar. Both ask to determine a frequency response and then take a inverse DFT to get the filter coefficients. So what's the difference?
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1answer
1k views

MATLAB center frequency shift

I am wondering how to shift the center frequency of the below complex data from 0, to say 20 MHz (10 MHz to 30 MHz- 20 MHz bandwidth). I tried to change the indexing of the bins but I could not get ...
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1answer
380 views

Splitting a magnitude across multiple bins in an IFFT

By Georg-Johann own work, CC BY-SA 3.0. I’m trying to synthesise a sine wave using an IFFT at a frequency between bin centre frequencies. Here are the details ...
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2answers
713 views

Sine Wave Aliasing during IFFT

I’’m synthesising a simple sine wave using the IFFT. I’m controlling the pitch of the sine wave by controlling the bin number and the phase for that bin number. I’ve synthesised an F whose ...