New Sensors Detect Speech Without Sound

Annoyed by cell phone users who believe they need to yell into their mobiles in order to be heard? Such loud and obnoxious talkers may become extinct, thanks in part to the military's need for sure -- and sometimes silent -- communications.

For years, scientists at the U.S. military's Defense Advanced Research Projects Agency, have been investigating ways to improve radio communications among troopers in noisy environments such as inside a rumbling tank or clattering helicopter.

Under its Advanced Speech Encoding project, DARPA hopes the answer may lie in refinement of so-called "non-acoustic sensors," experimental devices that can pick up a person's voice without a single syllable shouted, spoken or otherwise uttered.

One such device, the Tuned Electromagnetic Resonance Collar or TERC, being developed by a team of researchers at Worcester Polytechnic Institute in Massachusetts uses a unique approach to creating speech from an unspoken voice.

A Quest for Quiet Talk

TERC is a plastic strip embedded with thin copper foil and other small electronic components. When strapped around a person's neck, the collar acts as a big capacitor -- an electronic component that can be charged to hold a small amount of electricity.

As a person speaks, the tiny movement of the vocal chords changes the collar's capacitance. Microchips can measure and process these shifting electronic signals and turn them into synthesized human speech using computers equipped with specially crafted software.

The main advantage of non-acoustical sensors such as TERC is that they pick up only the sound of only the speaker wearing the device. Conventional microphones, by contrast, pick up the speaker's voice as well as every other sound within its range.

It's a novel approach to battling background noise, says Donald R. Brown, a principal investigator with the research team developing the sensor at WPI. But human capacitance is a technology that is well understood and already employed in other devices.

"If you own an iPod, the front switches work on capacitance technology," says Brown. "Drag your finger across it and it changes the capacitance and [the iPod] performs an action." Capacitance technology is also used in some laptop "touchpads" to control the on-screen cursor.

Sticky Points for a Collar

But WPI researchers admit that there are limitations to TERC that still need to be ironed out.

For one, the capacitance technology doesn't yet work across the entire range of dynamic human speech. Researchers note that TERC can't pick up fricatives (the "s" sound in "English," for example) and plosives -- the "p" sound in "pit."

Another harsh reality: While TERC can measure "glottal activity" for signs of a person speaking, it still takes a lot of bulky computers to translate those digital signals into recognizable speech. And what a receiver actually "hears" from a TERC-based transmission will be a computer-generated voice since the non-acoustic sensors don't capture the actual sound of the person speaking.

WPI's Brown says that while the initial research work on TERC is promising, DARPA funding for further study has lapsed. And the initial team of professors and graduate students researching the project has moved on to other areas. But he's hoping that both can be corrected this year.

One thing that could work in WPI's favor is Brown's belief that the TERC technology can be used for other purposes besides clear communications.

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