Hierarchical Active Voice Detection

One or more audio signals are processed using a multi-stage (hierarchical) voice and/or signal activity detector (VAD/SAD). A first stage is capable of reducing the workload bandwidth by employing an inexpensive VAD/SAD processor. One or more subsequent stages may further process the audio signals from the first stage. Other implementations may include a first stage that also performs continuity preservation between last blocks of audio signal and the first blocks of audio after it is detected that relevant audio signals are resumed. In yet other implementations, the first stage may extract features from audio signals when they are presented in their coded domain, and possibly with little or no decoding of the audio signal.