Effect on LTAS of vocal loudness variation

Area of Science:

• Speech Science
• Acoustic Phonetics
• Voice Analysis

Background:

• Long-term-average spectrum (LTAS) is a valuable tool for voice analysis, assessing voice source and formant characteristics.
• LTAS contours are known to be non-uniformly influenced by vocal loudness, posing challenges for consistent analysis.

Purpose of the Study:

• To analyze the non-uniform effect of vocal loudness on LTAS contours.
• To establish a method for predicting LTAS at various loudness levels and ensure reliable voice comparisons.

Main Methods:

• 15 male and 16 female untrained subjects read a text 7 times at varying vocal loudness levels.
• Overall equivalent sound level (Leq) changes averaged 27.9 dB (female) and 28.4 dB (male).
• Spectrum level was correlated with Leq up to 4 kHz, and gain factors were calculated based on frequency.

Main Results:

• Spectrum level showed a strong, linear correlation with Leq across all subjects up to 4 kHz.
• Gain factors varied with frequency (0.5 at low frequencies to 1.5 between 1.5-3 kHz).
• LTAS contours could be predicted with 2-3 dB accuracy below 4 kHz using subject-specific gain factors.

Conclusions:

• Vocal loudness significantly impacts LTAS, but this effect can be quantified and predicted.
• Accurate LTAS comparisons are feasible if recordings encompass a range of loudness levels.
• This research provides a framework for more robust voice analysis, particularly in clinical settings like pre- and post-voice therapy assessments.