The present paper proposes a new algorithm for pitch modification which is convenient for changing the fundamental frequency of speech with so fine resolution that is at least comparable with human pitch perception. Using the proposed method, measurements of just noticeable changes on speech prosody becomes possible. High resolution F0 manipulation is completed without explicit over-sampling of the signal, our FFT-based fast interpolation technique is used instead. Our algorithm is based on LP-PSOLA method. Although its frequency resolution was enhanced especially for research purposes it is possible that the need will arise from real applications of expressive speech synthesis in the future.