Laura Enflo

Vocal fold collision threshold pressure: An alternative to phonation threshold pressure?

Abstract Phonation threshold pressure (PTP), frequently used for characterizing vocal fold properties, is often difficult to measure. This investigation analyses the lowest pressure initiating vocal fold collision (CTP). Microphone, electroglottograph (EGG), and oral pressure signals were recorded, before and after vocal warm-up, in 15 amateur singers, repeating the syllable /pa:/ at several fundamental frequencies with gradually decreasing vocal loudness. Subglottal pressure was estimated from oral pressure during the p-occlusion, using the audio and the EGG amplitudes as criteria for PTP and CTP. The coefficient of variation was mostly lower for CTP than for PTP. Both CTP and PTP tended to be higher before than after the warm-up. The results support the conclusion that CTP is a promising parameter in investigations of vocal fold characteristics.

Collision and Phonation Threshold Pressures Before and After Loud, Prolonged Vocalization in Trained and Untrained Voices

The phonation threshold pressure (PTP) is defined as the lowest subglottal pressure needed for obtaining and sustaining vocal fold oscillation. It has been found to increase during vocal fatigue. In the present study, PTP is measured together with the threshold pressure needed for vocal fold collision; henceforth, the collision threshold pressure (CTP). PTP and CTP are compared before and after loud, prolonged vocalization in singer and nonsinger voices. Ten subjects repeated the vowel sequence /a, e, i, o, u/ at a Sound Pressure Level of at least 80 dB at 0.3 m for 20 minutes. Audio and electroglottography signals were recorded before and after this exercise. At the same time, oral pressure was registered while the subjects produced a diminuendo repeating the syllable /pa:/, thus acquiring an approximate of the subglottal pressure. CTP and PTP increased significantly after the vocal loading in the nonsinger subjects. On the other hand, singers reported no substantial effect of the exercise, and most singers had a mean after-to-before ratio close to 1 for both CTP and PTP.

The Impact of Glottal Configuration on Speech Breathing

OBJECTIVE The purpose of this study was to examine whether changes in respiratory patterns occurred in response to volitional changes in glottal configuration. METHODS Twelve vocally healthy participants read a passage while wearing the Inductotrace respiratory inductive plethysmograph, which measures the excursions of the rib cage and abdomen. Participants read the passage 5 times in a typical speaking voice (baseline phase), 10 times in an experimental voice, which was similar to a breathy vocal quality (experimental phase), and 5 times again in a typical speaking voice (return phase). Kinematic estimates of lung volume (LV) initiation, LV termination, and LV excursion were collected for each speech breath. RESULTS Participants spoke with larger LV excursions during the experimental phase, characterized by increased LV initiation and decreased LV termination compared with the baseline phase. CONCLUSION In response to volitional changes in glottal configuration, healthy individuals spoke with increased LV excursion. They both responded to changes (decreasing LV termination) and planned for more efficient future utterances (increasing LV initiation) during the experimental phase. This study demonstrated that respiratory patterns change in response to changes in glottal configuration; future work will examine these patterns in individuals with voice disorders.

Comparing Vocal Fold Contact Criteria Derived From Audio and Electroglottographic Signals

OBJECTIVES Collision threshold pressure (CTP), that is, the lowest subglottal pressure facilitating vocal fold contact during phonation, is likely to reflect relevant vocal fold properties. The amplitude of an electroglottographic (EGG) signal or the amplitude of its first derivative (dEGG) has been used as criterion of such contact. Manual measurement of CTP is time consuming, making the development of a simpler, alternative method desirable. METHOD In this investigation, we compare CTP values measured manually to values automatically derived from dEGG and to values derived from a set of alternative parameters, some obtained from audio and some from EGG signals. One of the parameters was the novel EGG wavegram, which visualizes sequences of EGG or dEGG cycles, normalized with respect to period and amplitude. Raters with and without previous acquaintance with EGG analysis marked the disappearance of vocal fold contact in dEGG and in wavegram displays of /pa:/-sequences produced with continuously decreasing vocal loudness by seven singer subjects. RESULTS Vocal fold contact was mostly identified accurately in displays of both dEGG amplitude and wavegram. Automatically derived CTP values showed high correlation with those measured manually and with those derived from the ratings of the visual displays. Seven other parameters were tested as criteria of such contact. Mainly, because of noise in the EGG signal, most of them yielded CTP values differing considerably from those derived from the manual and the automatic methods, although the EGG spectrum slope showed a high correlation. CONCLUSION The possibility of measuring CTP automatically seems promising for future investigations.