Development of an Acoustic Diagnosis Method Using an Analytical Model of the Vocal Tract

Abstract

Diseases occurring near the vocal cords, such as laryngeal cancer, share the initial symptom of hoarseness of voice. The GRBAS (grade, roughness, breathiness, asthenia, strain) scale is used as an acoustic diagnostic method for these diseases, but its objectivity is not well established. Instead, more accurate diagnosis may be possible by capturing the waveform of the flow velocity at the vocal cords. The aim of this study is to enable voice disturbances to be diagnosed by identifying the sound-source waveform from voice measurements. For acoustic analysis of the vocal tract, we modeled the air inside it as concentrated masses connected by linear springs and dampers. We identified the shape of the vocal tract by making the natural frequencies of the analytical model correspond to the measured formant frequencies, and we calculated the sound-source waveform from the measured voice waveform. The validity of the proposed method was confirmed by numerical simulation and an experimental device that simulates the human voice mechanism and comprises an acrylic vocal tract and a piston. We confirmed that the identified sound sources are similar to measured sound sources. We therefore conclude that our proposed methods are valid.