How can I use the function ifft for a range of values of time?

Hi. I have one vector with values of velocity for a range of frequencies and I have to pass this velocities for the time domain. I'd like to use the function ifft in this case, but I don't know how. When I applied the ifft in my vector of velocities, the program return one vector of the same length of the range the frequency, but I'd like to have one vector with these results of the velocities for one range of time especific. Help me, please! Thanks.

[Matt J]

The description of the "ranges" that you have is a little unclear. Does the range of frequencies you have cover the entire spectrum of velocities or just a part of it? If it's the entire spectrum, and assuming your sampling is good, the IFFT should give you a sampling of the entire time domain of interest. Why not just throw the unwanted time samples away?

Answer 1

[Wayne King]

Hi Marcia, If the velocity spectrum was obtained from the Fourier transform, then you have lost all time dependence. The Fourier transform integrates (sums) out the time variable.

Taking the inverse Fourier transform gives you the time record for the entire "signal"

However, once you obtain the time signal, you can now carry out a time-frequency analysis using the spectrogram() function in the Signal Processing Toolbox.

I don't know how large your dataset is, but the spectrogram is constructed by segmenting the time-domain data and Fourier transforming the segments (usually overlapped and windowed).

That gives you some time-frequency information on your signal. There are fundamental uncertainty limitations on how precise your picture can simultaneously be in both domains however.