Aerodynamic, Glottographic, and Acoustic Effects of Clear Speech: An Exploratory Study.

Objectives: The objective of the current study was to examine the acoustic, aerodynamic, and glottographic effects of Clear reading compared with Habitual reading.

Methods: Participants were five female and four male college students. They were native speakers of American English and had normal voice, speech, and hearing. Participants were instructed to read six sentences in four different conditions: (1) Habitual reading with a Glottal Enterprises mask off the face, (2) Habitual reading with the mask on the face, (3) Clear reading mask-off, and (4) Clear reading mask-on. Praat was used for acoustic analysis. The Glottal Enterprises system was used for airflow and oral air pressure recordings. A Kay Laryngograph was used to acquire the electroglottographic (EGG) signal. The airflow, air pressure, and EGG signals were analyzed using BGSigplot, implemented in MATLAB.

Results: The following measures increased significantly in clear reading compared with Habitual reading: (1) duration of sentences, stressed vowels, unvoiced fricatives, voice onset time for stop consonants, and stop gap in the second /p/ in the words papa, piper, and pepper; (2) fundamental frequency for vowels /ʊ/ and /ɛ/ for females; (3) intensity of stressed vowels and release of stop consonants; (4) oral air pressure in the phoneme /p/; and (5) airflow measures (average airflow, total air volume, and peak flow) in the words pass, cushion, papa, put, and pepper. The following measures did not change significantly in clear reading compared with Habitual reading: (1) fundamental frequency in male subjects; (2) glottal airflow measures, including closed quotient, open quotient (OQ), and skewing quotient; and (3) EGG measures, including EGG width, height, and contact and OQ.

Conclusions: Differences observed between Habitual and Clear readings suggest that clear speech predominantly involves changes in subglottal pressure and oral cavity kinematics rather than modifications in vocal fold adduction and vibratory dynamics.