Spectral modification technique in conversion of musical notes or tempos for singing voice synthesis system

Abstract

The STRAIGHT time‐frequency representations (spectrograms) of singing voice signals in various musical notes and various tempos are observed to develop a high‐quality synthesis system of singing voice. The spectrogram of STRAIGHT, which is a very high‐quality analysis‐synthesis system, can represent the vocal tract information accurately. A conversion system of a musical note or a tempo of an input singing voice signal has been implemented based on the observation. As a result of the observation, the frequency warping of the STRAIGHT spectrogram based on a DP matching algorithm has been introduced into the system. It was found that the method using a differential of a smoothed spectrum as a spectral distance measure in the frequency warping produces subjectively better quality than that using a smoothed spectrum directly. It was also found that the method without spectral modification, i.e., only with pitch/tempo modification in the conversion, produces better quality than that using a differential of a smoothed spectrum. This can be caused by the destruction of naturalness in the method using a differential of a smoothed spectrum.