Bell Labs' Audrey only recognized digits well for one trained voice

The first working speech recognizer, Bell Labs’ Audrey (1952), recognized the spoken digits zero through nine with an accuracy the original paper reported as 97 to 99 percent. The catch was speaker dependence: that accuracy held only after the analog circuit was adjusted to a particular person’s voice based on “some preliminary analysis of the speech of any individual.” Speaker independence - working for anyone off the street - would remain one of speech recognition’s hardest problems for decades.