1. A voicing estimation method for speech recognition implemented by a processor, the method comprising: performing a Fourier transform on input voice signals after the input voice signals are pre-processed; smoothing the transformed input voice signals based on a moving average of a spectrum and a predetermined number of taps considering male and females sexes; detecting peaks in the smoothed input voice signals; computing frequency bounds respectively associated with each of the detected peaks; and determining a voicing class according to each computed frequency bound.