### Voiced/Unvoiced Boundary Detection  
The methodology used to identify the voiced/unvoiced boundary in semi-automated RFF estimation requires further inquiry. First, it is unclear as to whether the three features used in aRFF and aRFF-AP algorithms are the best choice of acoustic features to mark the initiation and termination of vibration since voiced/unvoiced boundary detection accuracy has not been formally assessed amongst the three features or compared to that of other acoustic features (e.g., cepstral peak prominence). Second, there is uncertainty in how the boundary identified using these acoustic features corresponds to the physiological initiation or termination of vocal fold vibration. This is because both manual and semi-automated RFF methods rely only on the acoustic signal, which only provides indirect information about the vibration of the vocal folds and may be masked by supraglottic resonances, coarticulation (e.g., due to concurrent aspiration and friction), and radiation [27]. Thus--in addition to a lack of \(f_{o}\) stationarity during vocal fold offset and onset transitions--signal masking adds to the complexity of identifying the initiation or termination of vocal fold vibration. The uncertainties in acoustic boundary cycle identification warrant further investigation to (i) inform the implementation of acoustic features used in the semi-automated RFF algorithm and (ii) validate manual RFF estimation as a gold standard that accurately represents changes in instantaneous \(f_{o}\) during voicing offsets and onsets.  
High-speed videoundoscopy (HSV) may be a useful technique to examine the relationship between the acoustic signal and vocal fold vibration. By sampling at frame rates much greater than typical modal (i.e., the vocal register most typically used during conversational speech) \(f_{o}\) values, HSV can capture cycle-to-cycle changes in vocal fold vibratory behavior during voicing offsets and onsets [28; 29; 30]. Indeed, prior work has employed HSV to investigate voicing offsets and onsets relative to the acoustic signal: [PERSON] et al. [31] acquired simultaneous recordings via a microphone and rigid laryngoscope as vocally healthy speakers repeated /hi hi hi/ at their typical pitch and loudness. The results of this work indicated a tight coupling between the acoustic signal and the physiological vibrations of the vocal folds; however, this relationship may not be generalizable to the acoustic outputs typically examined with RFF. Transitioning between a vowel and the voiceless glottal fricative, /h/, may require different mechanisms than when transitioning between a vowel and a voiceless obstrut produced via oral constrictions (e.g., /f/, /s/, //, /p/, /t/, /k/). For instance, [PERSON] et al. [32] observed that glottal vibrations continued uninterruptedly through the /h/ during the production of /aha/ sequences by some speakers; these vibrations were not present for voiceless consonant productions of /asa/ or /apa/. Such differences could ultimately affect the relationship between oscillatory events obtained from the laryngoscopic images and from the acoustic signal. Additionally, the participants in [PERSON] et al. [31] were limited to adults with typical voices, whereas the target population for employing RFF in clinical voice assessments includes speakers with voice disorders characterized by excessive laryngeal muscle tension. As such, additional investigations are needed to examine voicing offsets and onsets in the context of speakers with and without voice disorders.