Machines that speak are nothing new. Siri has been answering questions from iPhone users since 2011, and text-to-voice programs have been around even longer. People with speaking disabilities—most famously, Stephen Hawking—have used computers to generate speech for decades. Yet synthesizing speech that sounds as natural as if spoken by a human is still an elusive goal, although one that appears to be getting closer to reality.
If you listen to the latest version of Apple's Siri, "it sounds pretty amazing," says Simon King, a professor of speech processing and director of the Centre for Speech Technology Research at the University of Edinburgh. Apple, Google, and Microsoft all have commercial speech applications that read text in a neutral but reasonable-sounding tone. Words are pronounced correctly, for the most part, and generally flow from one to the next in perfectly acceptable sentences. "We're quite good at that and the speech is very intelligible," King says.