## 4 Discussion
### Phonation Parameters
#### 4.2.2 Aerodynamic Parameters  
The energy transfer flow-tissue (R\({}_{\rm B}\)) between the two vibrational characteristics (Groups\({}_{\rm A}\)) increased by 12% to 12363 (Pa s\({}^{-1}\)). In [PERSON] et al. [39] R\({}_{\rm B}\) decreased continuously for increasing glottal gap (GGI\({}_{1-3}\)) by almost 50%. In contrast, here for GGI\({}_{1-2}\) R\({}_{\rm B}\) decreased by 30% and then increased by 5% for GGI\({}_{2-3}\). Compared to the data of [PERSON] et al. [39] the value of R\({}_{\rm B}\) for GGI\({}_{3}\) in this study was 42% higher; see Table 7. For GGI\({}_{1-2}\) our findings support other studies that higher energy transfer R\({}_{\rm B}\) from the glottal flow to vocal folds yields an improved acoustic quality (i.e., higher CPP values) [39; 60; 65]. Surprisingly, we found contrary results for GGI\({}_{2-3}\), that R\({}_{\rm B}\) was increasing/improving while CPP decreased/deteriorated even further; see Table 5. This discrepancy could be due to the fact that none of the other studies were investigating data containing solely disordered oscillations. Further investigations on disordered dynamics are required.  
The aerodynamic parameter SPL (dB) differs statistically significantly between the GGI groups, as well as between the two vibrational characteristics (Groups, Group\({}_{\rm A}\)); see Table 4. The intensity of the voice signal SPL (dB) decreases from Groups to Group\({}_{\rm A}\) by 16% from 78.1 dB to 65.9 dB, indicating that aperiodic oscillations (Group\({}_{\rm A}\)) are worse compared to subharmonic oscillations (Groups) in terms of efficiency/loudness of voice production.  
SPL also decreases from GGI\({}_{1}\) to GGI\({}_{3}\) by 22% from 76.7 to 59.5 dB (Table 5). This deterioration of SPL from GGI\({}_{1}\) to GGI\({}_{3}\) is stronger than for normal oscillations [39] from 79.1 to 69.4 (\(-\)12%). The general decrease in the intensity of the acoustic signal (SPL) may be explained by the fact that with a higher glottal gap index there is a limited oscillatory mobility of the vocal folds as well as an inadequate glottis closure and therefore sound is produced less efficiently.  
It is noteworthy that for GGI\({}_{3}\) 60% higher subglottal pressure than in [PERSON] et al. [39] was needed to produce the intensity of 59.5 dB, which is 14% lower than in the data of [PERSON] et al. [39]; see Table 7.  
Various studies investigated the influence of high subglottal pressure and irregular oscillation (i.e., disordered; Group\({}_{\rm S}\) and Group\({}_{\rm A}\)) in voice and rough phonation [28; 66; 67]. We cannot confirm these findings as the overall subglottal pressure regarding the irregular oscillations (Group\({}_{\rm S}\) and Group\({}_{\rm A}\)) here (Table 2) is 8% lower (1324 Pa) than that of the normal oscillations of [PERSON] et al. [39] (1436 Pa).  
However, we did find an interrelationship between high subglottal pressure and glottal closure insufficiency. The subglottal pressure P\({}_{\rm S}\) for GGI\({}_{1,2}\) was relatively similar comparing both studies while P\({}_{\rm S}\) for GGI\({}_{3}\) in this study was 60% higher compared to the normal oscillation data [39]; see Table 7. We assume that the combination of strong glottis closure insufficiency (GGI\({}_{3}\)) and disordered voices could be directly linked to high subglottal pressure. Unfortunately, previous studies on phonation data [28; 66; 67] did not examine the glottis closure insufficiency (i.e., GGI), which is why further investigations are needed to verify this assumption. Since the subglottal pressure data cannot be easily measured in humans, more ex vivo studies are hereby necessary.