Hello Muhammad Haziq Kamarul Azman,

if you have a phase shift between different frequencies, you can see it in the phase spektra but not in the magnitude spektra. Did you checked the phase spektra?

Otherwise when you do the phase shift for a single frequency during the time signal then, due to the linearity of the Fourier analysis, you will see no phase shift. Instead you will get additional high frequency artefacts.

Regards, Marinus

There are some Time Frequency Representations (TFR) invariants in the time-frequency plane, as for example the spectrogram. So you can use these TFR to evaluate time-shifts, which correspond to initial phase modifications.

That's a very interesting topic. I would say TFA tools are not theoretically shift invariant however the time/frequency shift might be Invisible due to the parameters applied (e.g. time segments and frequency bins).

Marinus Luegmair what should one expect to see on the phase spectra? If I understood my problem correctly, then I would expect to see changes in phase spectra value at the time instant of phase shifts, right? But will that happen only at the location of the frequency of the signal? Any ideas what to expect at frequencies not related to the signal?

Hello Muhammad Haziq Kamarul Azman, you shoud find a change in the phase spektra only for the frequency were a change happens. Nevertheless with a normal Fourier spectrum you wont get a change in the phase at the time point of the change, because of the averaging effect of the transformation. To get the time point you must use a TFR spectrogramm as recommended before.

Utilizing the short-time Fourier transform (STFT) for time-frequency analysis enables the examination of phase spectra. The interpretation of 'phase shifts' hinges on a specific context. STFT analysis accommodates the study of neural pulse trains and spontaneous cardiac electrical activity, both of which manifest themselves as biologically generated binary equivalent array signals. However, there are instances when preprocessing the original signal becomes essential to ensure an accurate assessment of phase shifts. For instance, consider that the information of interest might depend on the interval between pulses rather than the pulse sequence itself. Consequently, analyzing the phase shift within the 'distance between pulses' series could hold more significance than within the pulse train itself. Let me know if it is helpful. Peace and blessings.