Speech and Audio Signal Processing: Processing and Perception of Speech and Music, Second Edition

CHAPTER 4

BRIEF HISTORY OF AUTOMATIC SPEECH RECOGNITION

CONCEPTUALLY, the development of speech recognition is closely tied with other developments in speech science and engineering, and as such can be viewed as having roots in studies going back to the Greeks (as with synthesis). However, the history of speech recognition¹ per se in the 20th Century began with the invention of a small toy, Radio Rex.

4.1 RADIO REX

The first machine to recognize speech to any significant degree may have been a commercial toy named Radio Rex, which was manufactured in the 1920s. Here is a description from a 1962 review paper [18]:

It consisted of a celluloid dog with an iron base held within its house by an electromagnet against the force of a spring. Current energizing the magnet flowed through a metal bar which was arranged to form a bridge with 2 supporting members. This bridge was sensitive to 500 cps acoustic energy which vibrated it, interrupting the current and releasing the dog. The energy around 500 cps contained in the vowel of the word Rex was sufficient to trigger the device when the dog's name was called.

It is likely that the toy responded to many words other than “Rex,” or even to many nonspeech sounds that had sufficient 500-Hz energy. However, this inability to reject out-ofvocabulary sounds is a weakness shared by most recognizers that followed it. Furthermore, the toy was ...