Quiet or loud? Hand position matters when it comes to voice directivity

Holding a hand in front of your mouth creates a barrier that disrupts the normal propagation of sound waves. But by cupping your palms around your lips, that obstacle instead turns into a funnel for focusing noise.

While these effects may seem intuitive, accurately accounting for voice directivity is important for virtual and augmented reality. Pörschmann and Arend investigated the vocal phenomena with and without common hand postures in a systematic study.

“We found postures have more influence on voice directivity than any differences between phonemes,” said author Christoph Pörschmann. “So, if you’re looking at auralization of the human voice in virtual or augmented reality, it may be important to consider the influence of the postures.”

Subject were placed inside a spherical array of 32 microphones, where they sang a musical A with and without covering and cupping their hands around their mouth.

“We have some sparsity, as we measure only 32 directions, and there is some angle between them,” said Pörschmann. “If we directly spatially upsample this data to a dense set, the results are not exact, because the microphones cannot resolve the spatial complexity of voice directivity.”

This complexity arises because the sound emitted from the mouth is diffracted by the head and has a varying runtime to the microphones. The researchers used a spherical head model to equalize the signals and reduce the spatial complexity, allowing for more exact upsampling.

The authors believe hand postures could be detected by the tracking device of a head mounted display, which, in combination with the results of their study, would enable virtual and augmented reality applications to account for hand postures.

Source: “Effects of hand postures on voice directivity,” by Christoph Pörschmann and Johannes M. Arend, JASA Express Letters (2022). The article can be accessed at https://doi.org/10.1121/10.0009748 .