Several methods have been proposed for pitch estimation [18], among them the AUTOC (modified autocorrelation) method [18] is one of the most widely used. The AUTOC method first estimates the autocorrelation function, Φxx(m), of a clipped speech signal frame [18]. Next a threshold equal to 0.66Φxx(0), is applied to the estimated autocorrelation sequence. Finally the pitch period is given by the time interval between the consecutive points larger than a given threshold. Because it represents the periodicity or quasi-periodicity of speech segments, once the pitch periods have been estimated,the voiced segments can be easily determined. AUTOC method was chosen due to its low computational complexity and high precision in pitch detection.