Autumn 2004 / Leading Edge
The Sound of Silence

New technology for cellphones filters out background noise


It is the bane of cellphone users: the crackling background noise that makes it difficult to carry on a conversation. But a dual-microphone system developed at the University of Toronto may silence much of that annoying clatter.

“This system employs two microphones that, just like the two human ears, focus on the speaker’s voice to filter out other noises,” says Parham Aarabi, the lead researcher and a professor at U of T’s Edward S. Rogers Sr. department of electrical and computer engineering.

Time-frequency filters determine the speaker’s location, based on the length of time it takes for the most intense sound to arrive at the microphones. As the two microphones observe the speaker’s voice, a computer chip determines which frequencies belong to the speaker and which to extraneous noise. The interference is then “damaged” and its volume is scaled back. “Other speech-recognition systems only reduce the background noise, but this technology also deconstructs other conversations into a slight hum so they don’t confuse you,” says Aarabi.

While the dual-microphone system is currently too bulky to fit into cellphones, Aarabi predicts that a miniaturized version is about two years away. However, a customized chip that enhances voice recognition software in PCs is only months away.


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