Questions tagged [ifft]

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3
votes
1answer
415 views

Is it possible to reconstruct an image using its magnitude only?

Let us take any image like Lena or cameraman. I know that when Fourier transform is applied on image,spatially global features like amplitude and phase are obtained locally. My question is whether it ...
6
votes
2answers
457 views

Efficient calculation of correlation function every $N^{\rm th}$ point

I would like to calculate a long correlation function of length say, 1e6 points. I have a prior knowledge that the correlation peak will be in point k*1000. Is there an efficient way to apply this ...
0
votes
1answer
156 views

Microphone Array null steering unexpected results after IFFT

I am writing an open source microphone array simulation program:SharpEar. When I give uniform weight to microphone array elements, the result in the angle is a sinc function as expected. There are 41 ...
2
votes
2answers
941 views

Frequency Domain Filtering with big kernel size

I use FFT to do filtering in frequency domain, but when I use big kernel I got shift on border, I think it's due to nature of cyclical convolution and I need to do more zero padding. But how to ...
0
votes
1answer
843 views

Simple FFT convolution with impulse response wav file doesn't give the right results

I have been trying to find a solution to my FFT convolution problem but everything that I have found while searching hasn't been helping me. I have a working forward and backward FFT function, that I ...
0
votes
1answer
453 views

How to narrow the frequency band of a wavelet

I have a ricker wavelet with a dominant frequency of 15 Hz. The fourier transform shows its frequency band is almost to 50 Hz. How can I narrow the frequency band of this 15 Hz ricker wavelet? I have ...
0
votes
1answer
225 views

Conceptual question on FFT/IFFT (IFFT existence)

I was reading "Discrete and continuous Fourier transforms: analysis, applications and fast algorithms" written by E.Chu and, at some point, I found something that I could not completly understand. ...
1
vote
1answer
3k views

Using only positive frequencies in fourier domain, How will it affect the ifft?

I am going to do some kind of transformation and transform a data to another domain, and again back to the first domain. For this, I take a fourier transform of the data and separate the positive part ...
0
votes
1answer
769 views

Get data ready for IFFT

I am having troubles applying the IFFT function to some data I have. I already had a look here Complex conjugate and IFFT and here What assumptions should be used to invert spectrum into time domain ...
1
vote
2answers
504 views

Spectral location of individual OFDM symbols

The generic IFFT OFDM transmitter takes $N$ serial input data symbols, parallelizes them, maps them to their signal constellation points, and processes all $N$ resultant complex values using the IFFT ...
0
votes
1answer
180 views

Complex numbers in $\tt ifft$ of an MMSE amplitude estimator

I am trying to reconstruct a signal from a noisy speech using an MMSE algorithm proposed long time ago by Ephraim and Malah (1984). After going through the algorithm, I got a matrix A which represents ...
2
votes
2answers
924 views

Is magnitude information enough to reconstruct an audio signal

I have used an MMSE STSA estimator to obtain the magnitude of an audio signal. The original signal is combined with white noise and I used an algorithm given in an old research paper by Ephraim and ...
0
votes
0answers
295 views

Problem executing RIFFT in Cortex-M4

I'm implementing an Speech Recognition System over a Cortex-M4 processor (STM32F4-Discovery) and I'm facing a problem when a compute the RIFFT. I believe that I'm passing to the function the vector ...
0
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2answers
2k views

Inverse fourier transform by using a random phase and an original magnitude (matlab)

I want a image. Firstly I want to do fourier transform and get the magnitude and phase information. And then make a new random phase, finally use the changed random phase and original magnitude to ...
-1
votes
1answer
5k views

fft of a complex signal

I am new to dsp and just have a vague understanding of fft process. i know fft is used to convert time to freq domain.... i need to generate a sequence of frequencies such that F=[F1,F2,.....Fn-1] ...
0
votes
0answers
787 views

Why does a phase shift in the frequency domain not produce a time delay in the time domain?

Suppose I have an input signal which represents a vehicle front suspension response that has been measured using an accelerometer. It is seen that the measured rear suspension response is effectively ...
3
votes
1answer
1k views

How does the number of frequency-domain sampling points influence the outcome of an inverse FFT?

Given some frequency-domain representation of an impulse response. How does the number of frequency-domain sampling points influence the outcome of an inverse FFT, if I keep the sampling frequency ...
0
votes
0answers
625 views

Inverse FFT data format with FFTW

I perform FFT of two real sequences using "two for the price of one" - array $x[n]$ and $y[n]$ is packed as a complex number - $z[n] = x[n] + j y[n]$ - using FFT2 and FFTW. I am able to decode the ...
3
votes
2answers
2k views

How to transmit the real+imaginary output of an IFFT over a transmission channel?

I'm working on a modem system using a 16-QAM scheme. The transmitter runs an IFFT to modulate the signal, and has a 12-bit DAC. The receiver runs an FFT to demodulate the signal, and has a 12-bit ADC. ...
1
vote
2answers
619 views

fft(x) different from fft(ifft(fft(x))?

I normalized the spectrum of a time series and windowed the spectrum, then something strange happened. The code below can run in MATLAB or Octave. ...
4
votes
2answers
854 views

Alamouti code after or before IFFT block in OFDM

We are trying to implement Alamouti STBC on underlying ofdm signal. We were thinking as to where to write alamouti coder block. I thought we could write it after the cyclic prefixer block as we get a ...
0
votes
1answer
472 views

A problem about whitening of a signal

I intend to whiten the spectrum of a time series using a point-wise normalization in the frequency domain. In my first test, it looks pretty good. ...
0
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1answer
1k views

Bit reversal on twiddle factors on inverse FFT

I am currently working on a application which requires an inverse Fourier transform (IFFT) and am using a function library provided by Texas Instruments, in the datasheet they give an example on how ...
0
votes
1answer
2k views

IFFT and OFDM upconversion

I am trying to understand some basic concepts with IFFT as represented here OFDM Modem page 50-53, and 108-114. Some basics that are represented - The base sampling rate is 8khz. The symbol period ...
1
vote
3answers
2k views

Calculation of cosine in frequency domain instead of calculatin in time-domain followed by a FFT

I got an $N$, in my case 512, point FFT of a real-valued signal. Based on some calculation in my application I determine the parameters $k \in [1, N-1]$, the number of oscillations per period, $\phi \...
1
vote
1answer
155 views

Method for modifying frequency-domain signal to produce predetermined time-domain signal

We are performing a convolution of audio signal, with 511th order FIR filters, using fast convolution methods: overlap-add or overlap-save. Filters are being designed in frequency domain several ...
2
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0answers
91 views

Signal Relationships and Conversion: Transforming one Signal into another?

I'm trying to relate a near shore tidal signal (point A) to 3 points along a long model boundary (points B C D). I want to possibly have a relationship between B C D with which we can convert A ...
4
votes
2answers
666 views

What assumptions should be used to invert spectrum into time domain data?

This question comes from a realistic problem that how to obtain a time domain wind pressure from known wind spectrum. Or similarly, gets rail surface curve from spatial rail spectrum. Obviously, ...
6
votes
2answers
3k views

Filter size vs. FFT size and Overlap add

First of all I would like to say that : I'm new to DSP and in a "learning curve" hence the "basicness" of my questions. I've read as many posts/articles as possible on the internet but still need "...
2
votes
3answers
2k views

ifft of signal without phase information

I have a chemical spectrum with amplitude on the Y axis and wavenumbers on the X axis, sampling interval I think this is $1.5^{...
0
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1answer
159 views

Inverse Fast Fourier Transform Hard Way

I'm reading "Digital Signal Processing", written by Michael Weeks. In section Representing a Digital Signal as a Sum of Sinusoids, there is this Matlab code that I cannot understand. (code given below)...
4
votes
1answer
17k views

Cross correlation with FFT and fftshift

When I calculate the cross correlation between two vectors with the following code ...
1
vote
0answers
76 views

Get excitation from two signals

I have two signals, one whisper data and one normal voice data of the same sentence. I'm trying to build a voice conversion, but just want to start off with some simple signal manipulations. I ...
0
votes
3answers
427 views

inverse FFT when only a few time points are needed

I am developing C++ code to do some modeling that will take as input a parametric model of the complex frequency response (amplitude, phase) and produce as output an impulse response, e.g. using the ...
-1
votes
1answer
202 views

what I'll get if I take FFT of a frequency domain data

What I'll get if I take FFT of a frequency domain data. I have two questions related to this. For ex, x is a time domain data where X = fft(x), now fft(X)= what i'll get ? While reading SCFDMA, data ...
0
votes
1answer
416 views

spectral division

Sorry if this is elementary. If I add a small sinusoidal signal to my data and then take FFT of both my original and the modified one and then inverse FFT the division of the two, I should then be ...
1
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2answers
497 views

Image processing free open source libraries

This is the first time that I post a question here so excuse me for asking such a beginner question. what free open source <...
19
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4answers
23k views

Reconstruction of audio signal from Spectrogram

I have a set of songs for which I extracted the magnitude spectrogram using a Hamming Window with 50% overlap. After extracting the spectrogram, I did some dimensionality reduction using Principal ...
1
vote
2answers
2k views

what does the output of ifft in ofdm look like?

i have a problem in ofdm modulation .... there is a stream of bits that is converted from serial to parallel and is applied to an IFFT block. based on the definition of IFFT the output should be an ...
1
vote
1answer
3k views

Frequency response <-> Impulse response

I am trying to calculate an actual frequency response from a desired frequency response. fftSize = 128; fs = 8000; I have 2 input arrays: f[] and aDesired[], ...
8
votes
3answers
24k views

How to make a signal conjugate symmetric?

Take the simple frequency-domain band-pass filtering operation below . . . ...
0
votes
1answer
265 views

How do I implement IFFT to filter low frequencies from a group,after Freq detection by FFT?

I use a combination of Visual Basic Programming interfaced with FAMOS which is a DSP software like MATLAB but much easier. I am trying to separate signals from a group, which requires filtering each ...

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