Acoustic interpretation of the voice range profile (phonetogram)

The voice range profile (VRP) is a display of vocal intensity range versus fundamental frequency (F0). Past measurements have shown that the intensity range is reduced at the extremes of the F0 range, that there is a gradual upward tilt of the high- and low-intensity boundaries with increasing F0, and that a ripple exists at the boundaries. The intensity ripple, which results from tuning of source harmonics to the formants, is more noticeable at the upper boundary than the lower boundary because higher harmonics are not energized as effectively near phonation threshold as at maximum lung pressure. The gradual tilt of the intensity boundaries results from more effective transmission and radiation of acoustic energy at higher fundamental frequencies. This depends on the spectral distribution of the source power, however, At low F0, a smaller spectral slope (more harmonic energy) produces greater intensity. At high F0, on the other hand, a shift of energy toward the fundamental results in greater intensity. This dependence of intensity on spectral distribution of source power seems to explain the reduced intensity range at higher F0. An unrelated problem of reduced intensity range at low F0 stems from the inherent difficulty of keeping F0 from rising when subglottal pressure is increased.