## 2 Materials and Methods
### Data Analysis
#### 2.3.1 High-Speed Video Processing
The remaining 3.5% of cases were discarded due to producing inappropriate glottic angle estimates even after manual-assisted angle estimation (278 of 7999). This analysis resulted in 7721 usable /ifi/ productions for further processing. This initial data processing was then rechecked by a second technician. A series of kinematic time points were then extracted from each usable /ifi/ production to mark the physiological termination or initiation of vocal fold vibration. Technicians were presented with a MATLAB GUI showing time-aligned high-speed video frames, the microphone signal, the previously extracted glottic angle waveform, and a high-pass filtered version of the quick vibratory profile (QVP; see Figure 2). The QVP was included here as an alternative to the glottic angle waveform due to its sensitivity to HSV imagery and superior ability to track the vibrating glottis during the transition between voiced and unvoiced segments [29]. The QVP was calculated by (i) centering the HSV frame over the glottis using the semi-automated glottic angle extraction algorithm from [PERSON] et al. [38], (ii) calculating vertical and horizontal profiles of the HSV frames using the methodology from [PERSON] et al. [29], and (iii) high-pass filtering the resulting QVP using a 7 th order Butterworth filter to attenuate low frequency energy below a cut-off frequency of 50 Hz. With the MATLAB GUI, a total of three technicians used the time-aligned microphone signal, glottic angle waveform, and QVP to identify the time of voicing offset (t\({}_{\text{off}}\)) and the time of voicing onset (t\({}_{\text{on}}\)). For each participant, a single technician was assigned to identify t\({}_{\text{off}}\) and t\({}_{\text{on}}\) for all utterances. In this analysis, t\({}_{\text{off}}\) was described as the termination of the last vibratory cycle before the voiceless consonant, whereas t\({}_{\text{on}}\) was characterized as the initiation of the first vibratory cycle after the voiceless consonant. In the event that the vocal folds exhibited an abrupt closure at the start of voicing onset (i.e., prior to vocal fold vibration), t\({}_{\text{on}}\) was extracted as the time point immediately before the point of abrupt vocal fold closure. Technicians were instructed to use the glottic angle waveform and QVP to identify these two time points, then corroborate the selected indices via manual visualization of the raw HSV images. This process was carried out to minimize errors that may occur if the glottic angle waveform failed to capture small glottal gaps during vibratory cycle phases or if the QVP was confounded by lighting artifacts (e.g., intensity saturation due to the epiglottis coming into view). The microphone signal was included within the GUI to orient technicians in the event that the glottic angle waveform and QVP both failed to properly track the vibrations of the vocal folds; in such cases, the technicians were instructed to indicate that the production needed to be rejected or reprocessed. The technicians each reanalyzed 10% of participants in a separate sitting to ensure adequate intrarater reliability. The three technicians also analyzed the HSV images of  
Figure 2: (**a**) View of the vocal folds under flexible nasendoscopy, with the glottic angle marked from the anterior commissure to the vocal processes, (**b**) acoustic signal, (**c**) raw glottic angle waveform (gray) with smoothed data overlay (black), and (**d**) Filtered quick vibratory profile (QVP). The black dotted line in (**b–d**) indicates the current video frame shown in (**a**). The time of voicing offset (orange solid line) and time of voicing onset (teal solid line) are indicated in (**b–d**). the same participant to assess interrater reliability. Intrarater reliability was assessed via two-way mixed-effects ICCs for absolute agreement, whereas interrater reliability was computed using two-way mixed-effects ICCs for consistency of agreement (single measures). Intrarater reliability ranged from 0.86 to 0.99, with an overall mean reliability of 0.96 (SD = 0.05).