Given the normalized and filtered energy signal ( ) a derivative filter is used in order to enhance the speech/non-speech change-points. This processing helps prevent degradation due to low signal-to-noise ratios or nonstationary environments and was first introduced by Li et al. (2002). Such filter is defined via the following impulse response,
|Half of the window length.||(4.4)|
And the values of the coefficients , for a chosen window length . The selection of an appropriate value for the parameter is important as it sets the temporal resolution of the detector.
As shown in fig. 4.2 the result of the convolution of and , is thresholded and labelled, each sample, as speech or non-speech.