Harmonic Plus Noise Model Based Speech Synthesis in Hindi and Pitch Modification
نویسندگان
چکیده
In harmonic plus noise model (HNM), each segment of speech is modeled as two bands: a lower "harmonic" part represented as amplitudes and phases of the harmonics of a fundamental and an upper noise part using an all-pole filter excited by random white noise, with dynamically varying band boundary. HNM based synthesis can be used for good quality output with relatively small number of parameters and it permits pitch and time scaling without explicit estimation of vocal tract parameters. We have investigated its use for synthesis in Hindi which has aspirated stops and lacks voiced fricatives. The implementation used Childers and Hu's algorithm for voicing and pitch detection. It was found that good quality synthesis could be carried out, including those of aspirated stops. The upper band of HNM was needed only for the palatal and alveolar fricatives. To investigate the sensitivity of output quality to the errors in glottal closure instants, these were also obtained from output of an impedance glottograph, recorded simultaneously along with the speech signal. Random perturbations exceeding 4% of the local pitch period resulted in noticeable degradation. Synthesis with pitch scaling showed that the frequency scale of the amplitudes and phases of the harmonics of the original signal needed to be modified by a speaker dependent warping function, obtained by studying the relationship between pitch frequency and formant frequencies for the three cardinal vowels naturally occurring with different pitches in a passage with intonation.
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