The last dimension of your tensor is always to be 2 representing the real and complex parts of a data point. Suppose I have a data point of shape [1, 22, 313] representing 22 channels and 313 timesteps, then one way to go ahead would represent every number in the form of a + ib therefore making it of shape [1, 22, 313, 2] where the last dimension suggest 2 parts to every number in the datapoint.