1. A method of obtaining normalized voice activity detection features from an audio signal comprising the steps of: at a computing system, dividing an audio signal into a sequence of time frames; computing one or more voice activity detection feature of the audio signal for each of the time frames; computing running estimates of minimum and maximum values of the one or more voice activity detection feature of the audio signal for each of the time frames; computing input ranges of the one or more voice activity detection feature by comparing the running estimates of the minimum and maximum values of the one or more voice activity detection feature of the audio signal for each of the time frames; and mapping the one or more voice activity detection feature of the audio signal for each of the time frames from the input ranges to one or more desired target range to obtain one or more normalized voice activity detection feature.