Are Acoustic Markers of Voice and Speech Signals Affected by Nose-and-Mouth-Covering Respiratory Protective Masks?
Youri Maryn, Floris L Wuyts, Andrzej Zarowski
PMID 33608184WHAT IT FOUND
Masks change voice measurements, but not all equally.
A surgical mask barely affects pitch, loudness, or jitter, though it still skews quality scores. A transparent mask alters nearly every acoustic marker, including formants and high-frequency energy. Match mask types across pre- and post-treatment recordings.
Key findings
01A surgical mask left 16 of 26 acoustic markers unaffected, including fundamental frequency, sound intensity, jitter, shimmer, harmonics-to-noise ratio, and first and second formants.
02A transparent mask affected the most measures, significantly changing sound intensity, shimmer, harmonics-to-noise ratio, smoothed cepstral peak prominence, Acoustic Voice Quality Index, first formant, second formant, and second formant bandwidth.
03For clinical assessment, a surgical mask requires no adjustment to reference values for pitch, loudness, jitter, shimmer, harmonics-to-noise ratio, formants, spectral center of gravity, spectral standard deviation, or spectral slope, but quality indices like AVQI and CPPS shift significantly.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
The study used a mechanical mannequin head rather than human speakers, so it could not measure how masks affect actual speech movements, articulation, or noise from facial hair rubbing against the mask. Only three specific mask types were tested, so findings may not apply to cloth masks, masks with filters, or other designs. The model's loudspeaker and mouth opening may not perfectly replicate human anatomy, though the authors argued this design choice did not bias the comparison between mask conditions.
Declared interests
The authors declared no conflict of interest.
The easy way to misread this
Do not assume that a surgical mask is acoustically neutral. While it does not significantly change pitch, loudness, jitter, shimmer, or harmonics-to-noise ratio, it does significantly alter smoothed cepstral peak prominence and the Acoustic Voice Quality Index. If you rely on these quality indices for diagnosis or treatment tracking, a mask change between sessions can mimic or hide real change in voice quality.