ifft

Question

i Venky 2011-10-13

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https://ww2.mathworks.cn/matlabcentral/answers/18159-ifft

编辑： Mayank Lakhani 2015-7-8

I want to distort the phase of the frequency spectrum of a signal and not the magnitude. After that I want to find out the ifft considering both magnitude and the new phase. Usually I consider the function as a whole (complex function x) and find ifft(x). But I don't know how to find ifft of mag(x) and a*phase(x) (where 'a' is any constant).How would I do that?

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Answer 1

Honglei Chen 2011-10-13

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在 MATLAB Online 中打开

Let's assume that the signal is x. So what you could do is

Xf = fft(x);
Xf_mag = abs(Xf);
Xf_phase = angle(Xf);
% do whatever you need to the phase and save to Xf_phase_new
Xf_new = Xf_mag.*exp(1i*Xf_phase_new);
x_new = ifft(Xf_new);

HTH

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David Young 2011-10-13

Thanks, my comment deleted as now irrelevant.

i Venky 2011-10-14

Didn't even realize this. Thanks man.

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Answer 2

Mayank Lakhani 2015-7-8

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https://ww2.mathworks.cn/matlabcentral/answers/18159-ifft#answer_185378

编辑：Mayank Lakhani 2015-7-8

Hi all, I want to have amplitude and phase reconstruction of the signal. My signal is having 40KHz bandwidth and starting frequency is 70Khz to 110 KHz. Suppose my signal is X.

nfft = length(x);

res = fft(y_filt,nfft)/ nfft; % normalizing the fft

f = fs/2*linspace(0,1,nfft/2+1); % choosing correct frequency

res = res(1:nfft/2+1); % amplitude of fft

res2 = fft(res);

now i want to plot frequncy versus amplitude and frequency versus phase. figure, plot(f,abs(res2) where the amplitude shoud be lying from the 70KHz to 110 Khz and same in the Figure(f,angle(res2), the phase shoud be spreaded over 70kHz to 110Khz. So how to chose the correct frequency axes.