Playback attack is an illicit attempt to acquire unauthorized access to the automatic speaker verification (SV) system by using pre-recorded speech samples of the target. It is a widely acknowledged fact that state-of-the-art SV systems are quite vulnerable to playback attacks, and developing detection system is currently a burning issue. Based on the review made on past works, we found that most of them try to capture the trace of the playback device characteristics by using spectral related information that remain almost intact in pre-recorded signals, resulting less improvements in false acceptance rate. In this work we proposed an alternative approach for detecting playback signals. By proper analysis of the pre-recorded signal we observed that the playback device characteristics significantly affect the spectral patterns in the low frequency regions, around (0-400 Hz), and in this region the excitation source information is dominantly present. This motivates us in exploring the excitation source information for detecting playback signals. To further strengthen our conjecture we made spectral level analysis and speaker verification experiments. We observed that, as compared to spectral related vocal-tract information, the excitation source information is relatively more robust against playback attacks. In future, we will explicitly model the excitation source signals and derive suitable parameters for the development of playback attacks detection system.