With the recent advances in speech signal processing techniques, the need to detect the presence of speech accurately in the incoming signal under different noise environments has become a major concern of the industry. The separation of speech segment from the non-speech segment in an audio signal is achieved using a Voice Activity Detectors (VAD). VAD’s are a class signal processing methods that detects the presence or absence of speech in short segments of audio signal. A VAD has a pivotal role as a preprocessing block in wide range of speech applications. An integrated VAD in speech communication system, improves channel capacity, reduces co-channel interference and power consumption in portable electronic devices in cellular radio systems and allows simultaneous voice and data applications in multimedia communications. In slowly varying non-stationary environments where speech is corrupted by noise, a VAD is used to learn noise characteristics and estimate the noise spectrum. ... Это и многое другое вы найдете в книге A survey and evaluation of voice activity detection algorithms (Sameeraj Meduri and Rufus Ananth)