1. An apparatus for detecting a voice activity period, comprising: a domain conversion module converting an input signal into a frequency domain signalin a unit of a frame of the input signal; a subtracted-spectrum-generation module generating a spectral subtraction signal by subtracting a noise spectrum from the converted frequency domain signal; a modeling module applying the spectral subtraction signal to a probability distribution model to yield a calculated probability distribution; and a speech-detection module determining whether a speech signal is present in a current frame based on the calculated probability distribution.