There are 2.5 million people in the U.S. with severe speech disorders, and some 40 percent of them use speech devices to express themselves. But those devices offer an extremely limited selection of computerized voices.

“We wouldn’t dream of fitting a little girl with the limb of a grown man — so, why then, a prosthetic voice?” asked Northeastern University professor Rupal Patel in a talk at the TEDWomenconference in San Francisco last week.

Over the past six years, Patel has developed a process for morphing voices in which she combines samples of a patient’s speech — however limited it may be — with the voice of a donor who shares similar age, gender, size and location.

From the recipient, she extracts pitch, loudness and sibilance. As little as a single vowel may be enough. From the donor, she records a list of hundreds of utterances, which in the lab can be broken down to individual phonemes.