FFT and IFFT: Random Phases

Question

I imported a single audio file to MATLAB workspace.   After I apply the FFT:     How can I random change the audio phases before apply the Inverse FFT and get the 'new_signal'? new_signal = ifft(Y) How can I do it?

Neeta Dsouza · Accepted Answer

here is what I used to randomize an array of timeseries data:
 
function randX = phaseRandomize(X)
% Returns a phase-randomized version of the input data X. If X is an array,
% each row is treated as an independant time series, and columns represent
% sample points. 

[N,L]=size(X);
Y=fft(X,[],2); % Get spectrum

% Add random phase shifts (negative for conjugates), preserve DC offset
rnd_theta= -pi + (2*pi).*rand(N,L/2-1); 
Y(:,2:L/2)=Y(:,2:L/2).*exp(1i*rnd_theta);
Y(:,L/2+2:L)=Y(:,L/2+2:L).*exp(-1i*flip(rnd_theta,2));

% return phase-randomized data
randX =ifft(Y,[],2);
end

FFT and IFFT: Random Phases

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