What is the effect of padding zeros to FFT on time domain ? (opposite of what is usually done) As above. I know that zero padding in time increasaes frequency resolution but I'm having a hard time to understand the opposite. How would you interpret that?
The same effect will happen on the time-domain sequence too, due to the fact that DFT time and frequency domains are exact duals apart from a scaling factor and reversal.

Therefore, by properly zero padding (to the center of) the FFT data, the corresponding time-domain signal will be interpolated; i.e., more samples from the same signal will be obtained.