Dear Dr. Hilger,

1. Use of CO2-range as a “respiratory-effort” proxy. Please define precisely what you mean by “effort” (air-flow? sub-glottal pressure? lung-volume change), as noted by R2. Cite evidence that exhaled-CO2 dynamics capture that construct, or add a direct airflow / pressure measure; otherwise restrict conclusions to speculation.

2. Clarify glottal-gap measurement and reliability. Please explain that gap was recorded in a separate laryngoscopy session on /i/ and discuss its applicability to later aerosol tasks, as noted by R2. Further provide intra-/inter-rater reliability statistics and avoid calling a larger gap “phonatory efficiency” unless backed by flow/pressure data.

3. Improve acoustic predictors and control for loudness. Re-extract HNR (or a more suitable periodicity measure) from the head-mounted microphone used during aerosol capture, as noted by R2. Report sound-pressure levels per condition and separate HNR’s role as periodicity vs. turbulence indicator.

4. Statistical methods. Please consider re-fitting models with a canonical log link and include participant random effects to reflect repeated measures; a canonical log link is often preferred for lognormal means as the distribution is bounded below zero and skews right, whereas the identity assumes an unbounded distribution. 

plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

• A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.
• A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.
• An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols . Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols .

We look forward to receiving your revised manuscript.

Kind regards,

Steven R Livingstone

Academic Editor

PLOS ONE

Journal Requirements:

When submitting your revision, we need you to address these additional requirements.

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and

https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

2. Thank you for stating the following financial disclosure:

This study was made possible with funding from and partnership with the National Federation of State High School Associations and the College Band Directors National Association, as well as the Research and Innovation Office at the University of Colorado Boulder.

Please state what role the funders took in the study. If the funders had no role, please state: "The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript."

If this statement is not correct you must amend it as needed.

Please include this amended Role of Funder statement in your cover letter; we will change the online submission form on your behalf.

3. Thank you for stating the following in the Competing Interests section:

NO authors have competing interests

Please confirm that this does not alter your adherence to all PLOS ONE policies on sharing data and materials, by including the following statement: "This does not alter our adherence to PLOS ONE policies on sharing data and materials.” (as detailed online in our guide for authors http://journals.plos.org/plosone/s/competing-interests). If there are restrictions on sharing of data and/or materials, please state these. Please note that we cannot proceed with consideration of your article until this information has been declared.

Please include your updated Competing Interests statement in your cover letter; we will change the online submission form on your behalf.

4. Thank you for uploading your study's underlying data set. Unfortunately, the repository you have noted in your Data Availability statement does not qualify as an acceptable data repository according to PLOS's standards.

At this time, please upload the minimal data set necessary to replicate your study's findings to a stable, public repository (such as figshare or Dryad) and provide us with the relevant URLs, DOIs, or accession numbers that may be used to access these data. For a list of recommended repositories and additional information on PLOS standards for data deposition, please see https://journals.plos.org/plosone/s/recommended-repositories .

5. If the reviewer comments include a recommendation to cite specific previously published works, please review and evaluate these publications to determine whether they are relevant and should be cited. There is no requirement to cite these works unless the editor has indicated otherwise. 

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Yes

Reviewer #2: Partly

**********

2. Has the statistical analysis been performed appropriately and rigorously? -->?>

Reviewer #1: Yes

Reviewer #2: I Don't Know

**********

3. Have the authors made all data underlying the findings in their manuscript fully available??>

The PLOS Data policy

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English??>

Reviewer #1: Yes

Reviewer #2: Yes

**********

Reviewer #1: This is an automated report for PONE-D-25-11745. This report was solicited by the PLOS One editorial team and provided by ScreenIT.

ScreenIT is an independent group of scientists developing automated tools that analyze academic papers. A set of automated tools screened your submitted manuscript and provided the report below. Each tool was created by your academic colleagues with the goal of helping authors. The tools look for factors that are important for transparency, rigor and reproducibility, and we hope that the report might help you to improve reporting in your manuscript. Within the report you will find links to more information about the items that the tools check. These links include helpful papers, websites, or videos that explain why the item is important. While our screening tools aim to improve and maintain quality standards they may, on occasion, miss nuances specific to your study type or flag something incorrectly. Each tool has limitations that are described on the ScreenIT website. The tools screen the main file for the paper; they are not able to screen supplements stored in separate files. Please note that the Academic Editor had access to these comments while making a decision on your manuscript. The Academic Editor may ask that issues flagged in this report be addressed. If you would like to provide feedback on the ScreenIT tool, please email the team at ScreenIt@bih-charite.de. If you have questions or concerns about the review process, please contact the PLOS One office at plosone@plos.org.

Reviewer #2: The authors are commended for their study aiming to elucidate the actual voice-production related factors of aerosol generation. It sheds quite a bit of light on these mechanisms, and increases our knowledge of the topic considerably.

As I am a voice specialist, and not an aerosol scientist, I will confine my review to the aspects of voice production which have been discussed in the text, and will leave it to other reviewers to address the aerosol measurement methods used.

My main concerns arise over your use and discussion around your predictors/confounders, CO2 Range, NGG and HNR:

CO2 Range

* I have concerns over the reliance on this measure as a proxy for airflow (222-223 and elsewhere). Can you explain HOW this is a robust enough indicator of 'respiratory effort and lung volume', 'amount of air expelled', supporting this with literature? This seems to be a very, very important point as your analysis hinges on this, and how you have controlled for this (essentially, controlling for airflow - which would seem to be very important to really elucidate the mechanisms of aerosol production).

* 101-102: Please clarify what 'respiratory effort' means - is this regarding muscle activation, minute ventilation, respiratory rate? Also, do you mean 'lung volume EXPENDED'? Because speaking of 'lung volume' is usually understood to mean at what relative volume (TLC, RLV, etc).

* Line 443: Again, you are referring to 'higher lung volume' and it is unclear whether you mean a higher lung volume initiation (i.e. at 70% of TLC) or you mean a higher lung volume expenditure (i.e. 30% of VC)

Normalised Glottic Gap (NGG)

* It is important that you specify that you are talking about a normalised glottic gap at the point of MAXIMUM excursion of the vocal folds in their oscillation. Glottic gap is most often, to my mind, used to indicate the gap at the point of maximum closure - indicating glottic incompetence.

* It is important to acknowledge somewhere in the text that the NGG that you have measured was during laryngoscopy, and not at any other point. It is entirely possible that the true values of glottic gap were different during the aerosol measuring procedure. Also, you have only measured NGG during an /i/ vowel, and have not done this for the other vowels you have elicited.

* Getting the mean of three cycles is good - however, ideally the calculation of NGG procedure should be carried out by more than one person and an ICC reported for the raters (as it is, essentially, a visual-perceptual judgement task). I suggest, at a minimum, that at least a repeated sample be analysed and then reporting an intra-rater reliability statistic for this.

* Line 401: Here you refer to glottic gap as a proxy for phonatory efficiency, where in other sections you've used it as an indicator for glottic turbulence (of course, they can be related). However, glottic gap as you've defined it does NOT reflect phonatory efficiency. You are using this measure to reflect the maximum opening of the glottis during open phase. Had you defined it as the glottic gap during the closed phase, this would reflect glottic incompetence and would reflect phonatory efficiency. For a true determination of efficiency, you need measures of flow, pressure and loudness. Please reword this section.

*Throughout you have asserted that a higher NGG would lead to turbulence, but this needs a reference from the literature.

HNR

* At times you say that you are relying on HNR to identify the periodicity of the task (249), whilst at others you discuss using this metric as an approximation for turbulence at the glottis (108). Which is it?

* HNR is, of course, correlated with a periodic signal, but you can have a perfectly periodic vocal fold oscillation with a low HNR (think of breathy voice, the incomplete adduction of the vocal folds would lead to increased air turbulence and increased noise content, but the vocal fold oscillation may still be perfectly periodic). You could have measured periodicity with a jitter measure - not perfect, but as you are using sustained vowels, entirely appropriate. Either report true periodicity (using a time-based measure like jitter), or nuance/remove mentions of HNR as a quantification of periodicity (211, 249, 399-402).

* Additionally, a low HNR would indeed indicate a relative lack of harmonic strength - but this does not necessarily have to happen as a result of glottic-level turbulence. You have measured HNR during videolaryngoscopy… which is VERY problematic. You have not reported the background SPL of the room that this was carried out in (especially as you were using stroboscopy, which is noisy), and what the microphone's response curve was, etc. etc. I appreciate that measuring it during laryngoscopy at least gives you the opportunity to correlate the HNR with THAT specific voice production token - but then to use this later in your analysis (especially when the participants were wearing a head-mounted microphone of higher quality - you don't report the microphone used during the laryngoscopy) means that you cannot make claims as to the actual presence of turbulence DURING the aerosol measurement you are making. Could you address this, or could you use HNR from the recordings made during aerosol production?

* The reliance on HNR as a measure of periodicity is also problematic as you have not reported any controlling for loudness. A louder signal would, to my mind, increase the strength of the harmonics, and depending on the phonation type, might increase the proportion of harmonics vs noise in the signal. In fact, you don't report SPL at all (other than asking participants to target 70-75dB). This is a significant confounder and problematic. Can you address this in your discussion at least?

COMMENTS ON THE EXPERIMENTAL TASKS AND THEIR DESCRIPTIONS

* I am struggling to see how an /h/-onset vowel has a higher glottic gap than voiceless whispering. I think what you are talking about is that at the point of the articulation of the /h/ (a consonant), the vocal folds were partially adducted for the /h/ to provide the turbulence we hear as an /h/. This is not a glottic gap (as it is usually defined). If the /h/ is followed by a vowel, then the glottic gap would be measured during the vowel. I struggle to see how this could possibly be larger than for whispering, when the vocal folds are held open throughout the production of the task. Moreover, the /h/ articulation actually occurs for only milliseconds - and is then followed by (I presume) a normal voice quality vowel (? you have not specified - were you aiming at a breathy phonation quality?). This is likely why the /h/ onset task had a CO2 range fairly similar to the other vowel productions. However, if you were asking for a BREATHY phonation quality in this h-onset task, then this needs to be stated more clearly. This needs clarification throughout the text.

* Your descriptions of modal voice as having a 'fully closed' glottis (116-117) and glottal fry as having 'partially closed' glottis are wrong (also 129-131). I think you are aiming at closure quotient? In this, you would mean how long, relative to the total glottal cycle, the vocal folds are fully closed? This would be higher in fry, lower in modal, and possibly lower still in falsetto. But, all three voice conditions likely achieve full closure. Please reword this to reflect higher/lower closure quotient, predominent open phase/closed phase, etc.

* At times you refer to voicing (151 - 'loud voicing') and everywhere else - as 'speech' (all the figures, 216, 305) you refer to this as . For example, you refer to the whispered vowel condition as 'whispered speech' (218), and modal phonation as 'modal speech'. What you've described is NOT speech, it is loud/whispered vowels/phonation. Speech would involve articulation, and none of your tasks include articulation (save for the /h/ in the /h/-onset task). This was confusing as at several points I wanted to point out that a forced whispered SPEECH/or LOUD SPEECH would involve articulation and this would be a prime candidate for larger particles. I suggest renaming your tasks as:

Sustained vowels in the following registers/conditions:

* Glottal fry (or pulse register)

* Modal register

* Falsetto register

* H-onset (or 'easy onset') [or if it's breathy phonation, you need to say so]

* Loud modal register (comfortable +10dB - or do you mean 10dB louder than the others, i.e. 80-85dB? Please clarify)

* Voiceless (Force Whispered)

DISCUSSION

* Have you considered that NGG and the CO2 range (as a proxy for airflow) are actually interrelated, as a higher NGG would lead to higher transglottic airflows? How have you controlled for this? You do not discuss at any point that what each of these metrics is being utilised as a proxy for (airflow, turbulence, etc) has considerable overlap and really can't be treated as such distinct indicators at all. HNR is affected by loudness, which is impacted by airflow/subglottic pressure, which will impact the CO2 range. HNR will also be impacted by a larger glottic gap. There needs to be a discussion at some point that these predictors, these metrics, are not as independent as you have been presenting them. This should result in a more nuanced discussion of the mechanisms of aerosol generation.

* I do not see that you have successfully differentiated between the role of airflow turbulence and airflow more generally. This is very problematic in my view.

* Any discussion about 'whispering' and its relative safety/risk have to be nuanced with the fact that what you have elicited from your participants was a FORCED whisper (perhaps a 'stage whisper')... a whisper which was targeted to be as loud as the rest of the tasks (bar the 'loud phonation' task at +10db). I think that you basically touch on this in your discussion around lines 437-439, but it is worth noting that not every whisper is equal!

Minor -

Line 79 - in the oral cavity during speech, we have the movement and approximation of ALL the articulators (not simply the opening and closing of the mouth) - generating many opportunities for fluid film burst, etc

Line 86 - Loud speech and singing MAY be initiated by higher lung volumes (to capitalise on higher recoil pressures) but this is NOT a certainty, as loudness can be achieved by lower lung volumes accompanied by higher expiratory and adductory forces. Please rephrase/remove.

Line 90 - Somewhat proves the point of the above (and I presume would be due to higher glottic-level tension/the supraglottic compression we frequently see for people who phonate into low lung volumes) - If both high lung volumes and low lung volumes increases aerosol generation - what point are you making? Obviously breath-holding will decrease aerosol generation as there is no airflow. I suggest either combining talk of high lung volumes with low lung volumes - or leave this out.

Line 152: The vowel in 'sun' is incorrect. It should be /^/

184: If you're going to talk about the vocal processes, you might as well refer to the 'anterior commissure'.

**********

what does this mean? ). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy

Reviewer #1: No

Reviewer #2: No

**********

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/ . PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org . Please note that Supporting Information files do not need this step.

Attachments

Attachment

Submitted filename: report_10.1101+2025.03.16.25324059.pdf

Dear Dr. Hilger,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript by Dec 13 2025 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

• A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.
• A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.
• An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols . Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols .

We look forward to receiving your revised manuscript.

Kind regards,

Steven R Livingstone

Academic Editor

PLOS ONE

Journal Requirements:

If the reviewer comments include a recommendation to cite specific previously published works, please review and evaluate these publications to determine whether they are relevant and should be cited. There is no requirement to cite these works unless the editor has indicated otherwise. 

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

Reviewer #2: (No Response)

**********

2. Is the manuscript technically sound, and do the data support the conclusions??>

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously? -->?>

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available??>

The PLOS Data policy

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English??>

Reviewer #2: Yes

**********

Reviewer #2: Dear Authors,

This manuscript is MUCH, MUCH improved. Thank you for taking on all of my very, very detailed points! I have one or two tiny little points that still, to my mind, need addressing - but they are minor. Once these are addressed, I think this manuscript needs to be accepted (and I don't need to review it again).

Line 46 - Call me a stickler (which I'm sure you already have, lol) - but I'm not sure you can have 'voiceless phonation' since phonation is typically used to refer to vocal fold vibration. Here, and elsewhere, it might be better to call whispering a 'voiceless sound production', or even 'voiceless production'.

Line 50 - Following on from above, 'sustained sound production'

Line 137 - 'followed by MODAL PHONATION'

Line 159 - I only used /^/ since it's what I can produce on my keypad, but please use the real IPA symbol for this: /ʌ/

DISCUSSION

Line 458 - /h/-onset shouldn't have any wider glottal configuration during phonation (unless it encouraged a slightly breathier phonation style, which you weren't aiming at), and whispering doesn't have phonation. Maybe reword to 'wider glottal configurations' without the 'phonation'. I can see the h-onset NGG during the vowel was actually larger than for modal voice, but within the error bar (Figure 4). It's possible that the task did induce some participants to produce a slightly breathier voice quality? Anyway, you can probably make the same point by saying 'Tasks characterised by wider glottal configurations (e.g. whispering, loud phonation)

Figure 4 - Need to change the 'Loud Speech' labels to 'Loud Modal'

Line 461 - You elicited forced, 'high intensity' (line 162) whispering - so not sure you can really call this a 'quieter production' (especially without even relative SPL values to go on). Also, I'm not familiar with the other literature you cite (11,12) - was their whispering a loud, forced whisper or a whisper one might use to not be overheard. Are your findings really 'contrary to the common assumption that quieter productions carry lower risk'? This needs a bit of rewording

476-486 - I'm not sure that mentioning 'lung volumes' is necessary. Keep line 478 up until, 'therefore requiring initiation of phonation at a higher lung volume', which you can drop. Then you can remove 482-484. I think you can just say that loud voicing typically requires higher SG pressure and stronger expiratory force AND GREATER AIRFLOWS'. Then in 485, 'Because airflows were not recorded...'

498 - 'whispering, a voiceless PRODUCTION task'

509-517 - This does need some nuancing. As mentioned, not all whispers are equal! Line 510 might be better as, 'whispering, ESPECIALLY NOT A FORCED, STAGE WHISPER, is not necessarily a safer alternative...' You have not measured a 'confidential whisper', so, I'm not sure you can say that a clear, low intensity modal register is likely to generate fewer particles. I would be surprised if a genuine, 'confidential' whisper - produced with a similar airflow to modal voice - did not generate fewer particles than quiet modal voice as it would essentially be the same task without vocal fold contact. That said, since Joe Public probably does not know that there's a difference between a quiet whisper and a loud whisper, I think it does bear reporting that a whisper is not necessarily safe. However, I think this paragraph needs some stronger qualifications and caveats. I know you talk about this in the limitations section (line 539), but it needs an extra nod here.

Line 532 - NGG is anything but stable. It will vary over the course of a single vowel from onset to termination, across repetitions of the same vowel, vary at different pitches and intensities (as you say in 535 - instantaneous glottal area which is NGG). That said, intra-participant variation across tasks types are likely to be large enough that the metric is useful for your purposes. I think this is the point you are making?

**********

what does this mean? ). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy

Reviewer #2: No

**********

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

To ensure your figures meet our technical requirements, please review our figure guidelines: https://journals.plos.org/plosone/s/figures

You may also use PLOS’s free figure tool, NAAS, to help you prepare publication quality figures: https://journals.plos.org/plosone/s/figures#loc-tools-for-figure-preparation.

NAAS will assess whether your figures meet our technical requirements by comparing each figure against our figure specifications.

The influence of glottal and respiratory factors on aerosol emission during phonation

PONE-D-25-11745R2

Dear Dr. Hilger,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice will be generated when your article is formally accepted. Please note, if your institution has a publishing partnership with PLOS and your article meets the relevant criteria, all or part of your publication costs will be covered. Please make sure your user information is up-to-date by logging into Editorial Manager at Editorial Manager®  and clicking the ‘Update My Information' link at the top of the page. For questions related to billing, please contact billing support .

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Steven R Livingstone

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments: