Creating a Computer Voice That People Like
When computers speak, how human should they sound? This was a question that a team of six IBM linguists, engineers and marketers faced in 2009, when they began designing a function that turned text into speech for Watson, the company’s “Jeopardy!”-playing artificial intelligence program.
Eighteen months later, a carefully crafted voice — sounding not quite human but also not quite like HAL 9000 from the movie “2001: A Space Odyssey” — expressed Watson’s synthetic character in a highly publicized match in which the program defeated two of the best human “Jeopardy!” players.
The challenge of creating a computer “personality” is now one that a growing number of software designers are grappling with as computers become portable and users with busy hands and eyes increasingly use voice interaction.
Machines are listening, understanding and speaking, and not just computers and smartphones. Voices have been added to a wide range of everyday objects like cars and toys, as well as household information “appliances” like the home-companion robots Pepper and Jibo, and Alexa, the voice of the Amazon Echo speaker device.
A new design science is emerging in the pursuit of building what are called “conversational agents,” software programs that understand natural language and speech and can respond to human voice commands.
However, the creation of such systems, led by researchers in a field known as human-computer interaction design, is still as much an art as it is a science.
It is not yet possible to create a com- ‘Say this with feeling,’ ” he said.
For those like the developers at ToyTalk who design entertainment characters, errors may not be fatal, since the goal is to entertain or even to make their audience laugh. However, for programs that are intended to collaborate with humans in commercial situations or to become companions, the challenges are more subtle.
These designers often say they do not want to try to fool the humans that the machines are communicating with, but they still want to create a humanlike relationship between the user and the machine.
“Jeopardy!” was a particularly challenging speech synthesis problem for IBM’s researchers because although the answers were short, there were a vast number of possible mispronunciation pitfalls.
“The error rate, in just correctly pronouncing a word, was our biggest problem,” said Andy Aaron, a researcher in the Cognitive Environments Laboratory at IBM Research.
Several members of the team spent more than a year creating a giant database of correct pronunciations to cut the errors to as close to zero as possible. Phrases like brut Champagne, carpe diem and sotto voce presented potential minefields of errors, making it impossible to follow pronunciation guidelines blindly.
The researchers interviewed 25 voice actors, looking for a particular human sound from which to build the Watson voice. Narrowing it down to the voice they liked best, they then played with it in various ways, at one point even frequency-shifting it so that it sounded like a child.