1. A computer implemented method for estimating a fundamental frequency of a speech signal comprising: receiving within a processor a signal spectrum of the speech signal; filtering the signal spectrum within the processor to obtain a refined signal spectrum with an increased spectral resolution; computing a cross-power spectral density from an equation including a product of a first element as the refined signal spectrum and a second element as the unrefined signal spectrum; transforming the cross-power spectral density into the time domain to obtain a cross-correlation function; and estimating the fundamental frequency of the speech signal based on the cross-correlation function.