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Voice activity detector for receiving speech signal

2017-08-15 20:24  
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A voice activity detector has an input for receiving an outgoing speech signal transmitted from a speech system to a user and an input for receiving an incoming signal from the user. Both the outgoing and incoming signals are divided into time limited frames. A feature is calculated from each frame of the incoming signal and for forming a function of the calculated feature and a threshold.The 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 simultaneous 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- amplifier in order to amplify the weak analog signals (in the range 25-400 mW of an analog telephone line).The IC1 is connected as a retriggerable monostable multivibrator with the Tr2 discharging the timing capacitor C3, if the pulse train reaches the trigger input 2 of  IC1 with period less than the time: The output 3 of IC1 is active ON when an analog or digital signal is presented at the output and it drops to low level, TWgh seconds after the input signal has ceased to exist. The main uses of voice activity detector 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.Based on the function, it is determined whether or not the incoming signal includes speech. Means are provided to determine the echo return loss during an outgoing speech signal from the interactive speech system and to control the threshold in dependence on the echo return loss measured.



Speech activity detector for telephone lines