To assess and manipulate the vibrato in musical sounds, audio engineers either informally listen to the audio or visually inspect waveform envelopes or spectrographic representations. Unfortunately, detailed descriptions of the amplitude and frequency trajectories of harmonic partials are difficult to infer from audio spectrograms, which means quantitative information is limited. This paper describes a collection of signal processing methods and a toolbox for extracting and analyzing vibrato-related parameters from solo audio recordings. The Vibrato Analysis Toolbox (VAT) uses a method based on the Hilbert transform to extract the amplitude and frequency variations as feature tracks. A parameterization algorithm then extracts various descriptive parameters including vibrato depth, frequency, spectral centroid, relative amplitude-frequency modulation phase and time delay, and other relationships based on the vibrato tracks. Together, these parameters provide a quantitative characterization of vibrato. The VAT also provides visualization and resynthesis functions that enable users to interactively explore many musical features. Algorithms are written in the Matlab programming language for easy adaptation, enabling further development by researchers and developers. Applications include music performance pedagogy, musicological studies, music production, and voice analysis.
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