How is voice sound on TV or phone distorted through a face mask? After a year of listening to people talk through face masks, it appeared to me that the sound is not merely muffled, but it has a very specific and recognizable tinge and texture to it.
It reminds me less of sound through a muffling pillow, and more of old speech recordings from the 1950s.
This is apparent whether you listen, today, to recorded speech on TV or radio or through the phone. Sometimes you hear it in person too.
I suspect that the sound is not just muffled or low-pass filtered, but that there is more happening. Perhaps it's a band-pass? A notch? Are there non-linear or time-variant effects from turbulence due to the interaction between plosives and the fabric?
Has anyone looked into this?
There are many researches on the acoustic effect of masks since the pandemic. You can find them on the website of The Journal of the Acoustical Society of America and most of them are free to access.
Masks have selectivity on both frequency and spatial.
In frequency domain, masks react as low-pass filters that attenuate high frequencies significantly. Interestingly, different research gives different results. They are saying 1 kHz$^{[1]}$, 2 kHz$^{[2]}$ and 3 kHz$^{[3]}$ maybe due to different understanding about &quot;significantly&quot;.
In spatial domain, masks lead to reduced frontal sound radiation compared to the lateral or rear radiation at high frequencies$^{[2]}$.
Researchers also tested the effect of microphone placement. They placed microphones on the lapel, cheek, forehead, and next to the mouth$^{[1]}$. These differences are mostly caused by the spatial radiation pattern with a mask.
And of course, different masks have different acoustic effect according to their materials, weaves and types.
References

[1] Acoustic effects of medical, cloth, and transparent face masks on speech signals
[2] Impact of face masks on voice radiation
[3] Effects of face masks on acoustic analysis and speech perception: Implications for peri-pandemic protocols
[4] Acoustic effects of non-transparent and transparent face coverings

[5] Effect of masks on speech intelligibility in auralized classrooms