Truncation of an autoregressive (AR) signal in time-domain results in spectral leakage in the frequency domain and hence, the magnitude and phase spectra and the derivative of phase spectrum (DPS) are distorted. In this paper, we show that the DPS is the least affected one when a signal is truncated. In view of the fact that several important features of a signal are preserved in its phase and DPS, this result is expected to find useful applications.