Questions tagged [ifft]

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19
votes
4answers
22k 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 ...
10
votes
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....
2
votes
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 ...
0
votes
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 $...
13
votes
2answers
24k views

Intuitive explanation of cross-correlation in frequency domain

According to the cross-correlation theorem : the cross-correlation between two signals is equal to the product of fourier transform of one signal multiplied by complex conjugate of fourier transform ...
8
votes
3answers
23k views

How to make a signal conjugate symmetric?

Take the simple frequency-domain band-pass filtering operation below . . . ...
4
votes
2answers
844 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 ...
3
votes
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 ...
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^{...
1
vote
1answer
668 views

How do you construct common waveforms (square, sawtooth, triangle, noise) from sine wave partials using an IFFT?

In the lovely image below we see the addition of sine waves making a square wave. I am coding a wave table synthesiser and thought it would be great to get the user to be able to fiddle with the ...
1
vote
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?
0
votes
3answers
414 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 ...
4
votes
2answers
662 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, ...
4
votes
1answer
267 views

Zero padding effect on a FFT of gaussian noise

I have a gaussian noise $\nu(t)$ with variance $\sigma^2$. After a FFT I get $X(\omega)$. If now I do the IFFT on the $X(\omega)$ can I say that the result is still a gaussian noise of variance $\...
2
votes
2answers
848 views

Determining channel frequency response from measured data via IFFT

I've been working on a small system that transmits a linear chirp over the 35Hz-20kHz frequency range in a room and simultaneously records the transmitted signal with echoes (from the floor, walls, ...
1
vote
1answer
1k views

Computation of the Inverse DCT (IDCT) Using DCT Or IFFT

Is there a way to compute the inverse discrete cosine transform (type-2) by leveraging either a DCT, FFT, or IFFT algorithm? I have seen ways to compute the DCT using FFTs, and I've seen ways to ...
1
vote
1answer
476 views

Convolution in frequency space with fft and ifft -> num output samples?

Let's say you had two 1 second sound samples at 44.1khz, and you wanted to convolve them in frequency space. You FFT each one to get two arrays of complex numbers that each have 44100 items in them. ...
0
votes
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 $F_s= 44100\textrm{ Hz}$...
0
votes
0answers
144 views

Lost power while using FFT with apodizing mask

Previously I asked this question about FFT artifacts. The solution that is most easily implemented is using an apodizing mask on the original image, tapering the borders to zero making the image left-...
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 ...
0
votes
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 ...