FOR a long time speech-recognition software was poor, confirming the saying that computers find it difficult to do things humans do easily, and vice-versa. But lately it has got much better: most modern smartphones now have a host of voice-activated features which actually work. Not only can programs such as Google Now or the iPhone's Siri handle restricted tasks like finding a restaurant or dialling a phone number; smartphones are also getting much better at free-form speech recognition, such as taking dictated text-messages or e-mails. How did computers get so much better at understanding speech?
Almost any word can begin a sentence, so the first word in a sentence can be one of tens of thousands. If any word were as likely as any other in any position, a five-word utterance from a vocabulary of 20,000 words would have 3.2 x 1021 possibilities. Faced with such odds (and a sound signal degraded by cheap microphones, background noise and compression), the task would be impossible.
Read the rest of "How Speech-Recognition Software Got So Good" at Economist.