A Technique for Investigating On-Off Patterns of Speech

T h e object of this study is to investigate certain properties of speech pertinent to the problem of establishing the pattern of its presence and 1 2 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 19f>5 absence on a telephone circuit. Recent developments in telephony, such as t h e introduction of long circuits with appreciable delay and the increasing use of voice-operated devices, have prompted learning more about speech patterns, especially as they occur in conversation. 1 - 2 - 3 Although t h e task of detecting the presence of speech m a y seem at first to be an almost trivial problem, it is in fact very difficult. Speech has a large dynamic range, and its level frequently falls into the noise, even during segments audible to a listener. In addition, momentary interruptions due in part to stop consonants ( / p / , / t / , / k / , etc.) might cause a speech detector to indicate a silent interval whereas a listener would indicate a continuing flow of speech. Most existing designs of speech detectors employ a slow release, or hangover, to bridge such gaps, but an error equal to the hangover time is made every time t h e person actually stops talking. T h e method of detection which was investigated in this study will hopefully avoid some of t h e pitfalls of conventional detectors. I I . T H E DETECTION T E C H N I Q U E