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Telephone line for speech voice activity detection

2016-02-06 17:31  
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A telephone line or telephone circuit (or just line or circuit within the industry) is a single-user circuit on a telephone communication system. Typically this refers to the physical wire or other signaling medium connecting the user's telephone apparatus to the telecommunications network, and usually also implies a single telephone number for billing purposes reserved for that user.This circuit can be used in telephone lines for speech activity detection purposes. This detection is very useful in the case of half-duplex conversation between two stations-in the case of siroultaneous transmission of voice and data over the same pair of cables by the method of interspersion data on voice traffic, and also in echo suppressor devices. The circuit consists of a class-A amplifier to amplify the weak analog signals (25-400 mV).The IC1 which follows, is conneGted as a retriggerable monostable multivibrator with the  TR2discharging the timing capacitor C3, if the pulse train reaches the trigger input 2 of IC1 with period less than the time: THIGH ~ 1.1 R3C3. The output 3 of C1  is active on when an analog or digital signal is presented at the output, and it drops to a low level, THIGH, seconds after the input signal has ceased to exist.Voice activity detection (VAD), also known as speech activity detection or speech detection, is a technique used in speech processing in which the presence or absence of human speech is detected.The main uses of VAD are in speech coding and speech recognition. It can facilitate speech processing, and can also be used to deactivate some processes during non-speech section of an audio session: it can avoid unnecessary coding/transmission of silence packets in Voice over Internet Protocol applications, saving on computation and on network bandwidth.Voice Activity Detection (VAD) is a very important front end processing in all Speech.