On a Pitch Alteration for Speech Synthesis Systems

Speech synthesis can be classified into waveform coding, source coding, or hybrid coding by the synthesis method. Among these, waveform coding is especially suitable for high-quality speech synthesis. However, synthesis techniques using syllable or phoneme unit is not desirable since it fails to separate the excitation and the formant part to handle speech. Therefore, there is a need for a pitch alteration method to apply in synthesis using waveform coding. This study proposes a pitch alteration method that uses spectrum scaling after flattening the spectra by a sub-band linear approximation to minimize the spectrum distortion. A comparison with LPC (Linear Predictive Coding), Cepstrum and lifter function is presented to show the better performance of the proposed method. Estimation method seeks each of the distributions of the flattened signal and measures the degree of the flattened spectrum Signal, which is normalized, so the highest point amounts to zero, and the distribution of the signal, whose average is zero, is calculated. The results are presented by the spectrum distortion rate to estimate the performance of the proposed method. The average spectrum distortion rate kept below the average 2.12%, showing the proposed method’s superiority in comparison with the other existing approaches.