Vocal Harmonic Analysis Focusing on Singer Compatibility Using Modified Stockwell Transform with Appropriate Parameter Selection

Previous studies have indicated that differences in the compatibility of singers in choral singing can be observed in terms of the first and second vocal tract resonant frequencies. However, the distinctions in the spectrograms of vocal harmonics remain unclear. In this study, we utilize a modified version of the Stockwell transform (MST), which features adjustable four parameters for optimizing time-frequency resolution. We attempted to select suitable parameter combinations by observing the effects of varying each parameter of MST through 3D plots of the indicator values. This approach enables us to clearly visualize vocal harmonics and reveal the synchronization of vibrato within the range of the frequency of the first and second vocal tract resonance, highlighting instances of good compatibility between singers.