isn't padded). If length is given in the arguments and is longer
   than expected, "istft" will pad zeros to the end of the returned
   signal.
If "center" is "True", then there will be padding e.g.
   "'constant'", "'reflect'", etc. Left padding can be trimmed off
   exactly because they can be calculated but right padding cannot be
   calculated without additional information.
Example: Suppose the last window is: "[17, 18, 0, 0, 0]" vs "[18,
   0, 0, 0, 0]"
The "n_fft", "hop_length", "win_length" are all the same which
   prevents the calculation of right padding. These additional values
   could be zeros or a reflection of the signal so providing "length"
   could be useful. If "length" is "None" then padding will be
   aggressively removed (some loss of signal).
[1] D. W. Griffin and J. S. Lim, "Signal estimation from modified
   short-time Fourier transform," IEEE Trans. ASSP, vol.32, no.2,
   pp.236-243, Apr. 1984.
Parameters:
      * input (Tensor) --