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New sensor helps computers separate overlapping sounds

14 August 2015

In a noisy room, the human auditory system is able to focus on a single voice while filtering out background noise; computers are not so adept - until now.

The prototype sensor can separate simultaneous sounds coming from different directions using a unique distortion given by the slice of 'pie' that it passes through (image: Steve Cummer/Duke University)

However, a new approach by engineers at Duke University might soon improve the performance of computers in loud environments. They have developed a device using metamaterials and a compressive sensing technique to determine the direction of a sound and extract it from the surrounding background noise.

"We've invented a sensing system that can efficiently, reliably and inexpensively solve an interesting problem that modern technology has to deal with on a daily basis," says Duke University researcher, Abel Xie. "We think this could improve the performance of voice-activated devices like smart phones and game consoles while also reducing the complexity of the system."

The proof-of-concept device is essentially a plastic pie-shaped honeycomb split into dozens of slices. While the honeycomb openings may all look the same, their depth varies from hole to hole. This gives each slice of the honeycomb 'pie' a unique pattern.

"The cavities behave like soda bottles when you blow across their tops," says Duke University's Professor Steve Cummer. "The amount of soda left in the bottle, or the depth of the cavities in our case, affects the pitch of the sound they make, and this changes the incoming sound in a subtle but detectable way."

Incident sound waves are slightly distorted by the cavities, and that distortion has a specific signature depending upon what slice of the 'pie' they passed over. A microphone detects the sound on the opposite side of the device, and its signal is fed to a computer that is able to separate the jumble of noises based on these unique distortions.

The researchers tested their invention in multiple trials by simultaneously sending three identical sounds to the sensor from three different directions. It was able to distinguish between them with a 96.7 percent accuracy.

While the prototype is around 15cm wide, the researchers believe it could be scaled down for inclusion in handheld devices. Moreover, as it is made of plastic with no electrical, electronic or moving parts, it is both efficient and reliable.

"This concept may also have applications outside the world of consumer electronics," says Xie. "I think it could be combined with any medical imaging device that uses waves, such as ultrasound, to not only improve current sensing methods, but to create entirely new ones.

"With the extra information, it should also be possible to improve the sound fidelity and increase functionalities for applications like hearing aids and cochlear implants. One obvious challenge is to make the system physically small. It is challenging, but not impossible, and we are working toward that goal."

The work is described in a recent edition of The Proceedings of the National Academy of Sciences.

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