A method for independently modifying the time and pitch scale of acoustic signals, with an emphasis on speech signals is proposed in this paper. The algorithm developed here is based on Short Time Fourier Transform(STFT). The purpose of this paper is to devise a way to change the rate of a pre-recorded sound without altering the frequency content. Simply playing the sound at a different rate is not a solution. The frequencies would be distorted in proportion to the scaling factor, and at very low or high rates, would be very difficult to understand at all, let alone identify as human speech. Our approach is to sample the digital signal and then interpolate data points between our samples to produce a sound of the desired length. A slowed-down sound would have more points inserted between the samples than the original signal had, and a speeded-up sound would have fewer than the original. Performance of the proposed algorithm is demonstrated using spectrum plots.

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Speech Analysis Speech Processing Time Scale Modification Wavelet Packet Transform