This paper proposes a new technique for detecting pitch patterns which is useful for automatic speech recognition, by using a narrow band spectrum analysis. The motivation of this approach is that humans perceive some kind of pitch in whispers where no fundamental frequencies can be observed, while most of the pitch determination algorithm (PDA) fails to detect such perceptual pitch. The narrow band spectrum analysis enable us to find pitch structure distributed locally in frequency domain. Incorporating this technique into PDA's is realized to applying the technique to the lag window based PDA. Experimental results show that pitch detection performance could be improved by 4% for voiced sounds and 8% for voiceless sounds.