Collision Threshold Pressure : A novel measure of voice function Effects of vocal warm-up, vocal loading and resonance tube phonation in water

Sammanfattning: The phonation threshold pressure (PTP), i.e., the smallest amount of subglottal pressure needed to initiate and sustain vocal fold oscillation, is frequently difficult to measure due to the difficulty for some subjects to produce extremely soft phonation. In addition, PTP values are often quite scattered. Hence, the collision threshold pressure (CTP), i.e., the smallest amount of subglottal pressure needed for vocal fold collision, was explored as a possible complement or alternative to PTP. Effects on CTP and PTP of vocal warm-up (Paper 1), resonance tube phonation with the tube end in water (Paper 2), and vocal loading (Paper 3) were investigated. With the aim to accelerate the CTP measurement process, comparisons were made between CTP values derived manually and those derived by several automatic or semi-automatic parameters (Paper 4).Subjects were recorded at various F0 while phonating /pa:/-sequences, starting at medium loudness and continuing until phonation ceased. Subglottal pressure was estimated from oral pressure signals during the /p/ occlusion. Vocal fold contact was determined manually from the amplitude of the electroglottographic (EGG) signal (Papers 1 and 3) or its first derivative (dEGG) (Papers 2 and 4).Recordings were made before and after exercise: (Paper 1) Vocal warm-up was carried out in the 13 singers’ own habitual way. (Paper 2) Twelve mezzo-sopranos phonated on /u:/ at various pitches for two minutes before post-recording, and 15 seconds before each additional F0, into a glass tube (l=27 cm, id=9 mm) at a water depth of 1-2 cm.(Paper 3) Five trained singers and five untrained 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.Statistically significant results: (Paper 1) CTP and PTP decreased after warm-up in the five female voices. CTP was found to be higher than PTP (about 4 H2O). Also, CTP had a lower coefficient of variation, suggesting that CTP is a more reliable measure than PTP. (Paper 2) CTP increased on average six percent after resonance tube phonation in water.(Paper 3) CTP and PTP increased after the vocal loading in the untrained voices, with an average after-to-before ratio of 1.26 for CTP and 1.33 for PTP.(Paper 4) Automatically derived CTP values showed high correlation with those obtained manually, from EGG spectrum slope, and from the visual displays of dEGG and of dEGG wavegram.