Morphometric Differences of Vocal Tract Articulators in Different Loudness Conditions in Singing

Abstract

Introduction: Dynamic MRI analysis of phonation has gathered interest in voice and speech physiology. However, there are limited data addressing the extent to which articulation is dependent on loudness.

Material and methods: 12 professional singer subjects of different voice classifications were analysed concerning the vocal tract profiles recorded with dynamic real-time MRI with 25fps in different pitch and loudness conditions. The subjects were asked to sing ascending scales on the vowel /a/ in three loudness conditions (comfortable=mf, very soft=pp, very loud=ff, respectively). Furthermore, fundamental frequency and sound pressure level were analysed from the simultaneously recorded optical audio signal after noise cancellation.

Results: The data show articulatory differences with respect to changes of both pitch and loudness. Here, lip opening and pharynx width were increased. While the vertical larynx position was rising with pitch it was lower for greater loudness. Especially, the lip opening and pharynx width were more strongly correlated with the sound pressure level than with pitch.

Conclusion: For the vowel /a/ loudness has an effect on articulation during singing which should be considered when articulatory vocal tract data are interpreted.

Fig 1. Waveform (upper row) and audio spectrum (middle row) for the file after the first noise cancellation (Confon, left panel) and after the second noise cancellation (Adobe, right panel).

The waveforms include all three loudness tasks (mf = mezzoforte, pp = pianissimo, ff = fortissimo, respectively). The lowest row shows Long Time Average Spectra (LTAS) for both files, after the first noise cancellation (blue) and the second noise cancellation (red), respectively.

Fig 2. Measured distances in each frame of the MRI material (red arrows), as described previously in detail [–11,15].

The auxiliary lines are shown in green. LO (Lip Opening), JO (Jaw Opening), JP (Jaw Protrution) HPT (Highest Point Tongue), UE (Uvula Elevation), LP (vertical Larynx Position).

Fig 3. Scatter plots for all articulatory measures for subject 8, mf task.

The original first rating is shown on the x-axis and the repeated measurements for the same rater (blue) and a different second rater (red), respectively, on the y-axis. The grey line refers to equivalence.

Fig 4. Representative mid-sagittal vocal tract profiles from a baritone (subject 10) for the different loudness tasks (mf = mezzoforte, upper row, pp = pianissimo middle row and ff = fortissimo, lowest row) for the pitches G3 (196Hz, left), C4 (262Hz, middle) and E4 (330Hz, right), respectively.

Fig 5. Mean values for the lip opening, jaw opening, pharynx width and larynx position, respectively, with respect to fundamental frequency (Hz).

The green color refers to the sopranos, blue to mezzosopranos, red to tenors and grey to baritones. The differences in color intensity reflect the loudness condition: The darker the color, the louder the voice.

Fig 6. Jaw opening versus lip opening for the mean values across each fundamental frequency.

The green color refers to the sopranos, blue to mezzo-sopranos, red to tenors and grey to baritones. The symbols reflect the loudness condition: circles = mf, triangles = pp, squares = ff.

Fig 7. Mean values for sound pressure level (dB) with respect to fundamental frequency (Hz).

The green color refers to the sopranos, blue to mezzo-sopranos, red to tenors and grey to baritones. The differences in color intensity reflect the loudness condition: the darker the color, the louder the voice.