1. A method for determining a voicing probability of a speech signal comprising the steps of: generating an original speech spectrum S &ohgr; (&ohgr;) of the speech signal, where &ohgr; is a frequency; generating a synthetic speech spectrum &Scirc;&ohgr;(&ohgr;) from the original speech spectrum S 107 (&ohgr;) based on the assumption that the speech signal is purely voiced; dividing the original speech spectrum S &ohgr; (&ohgr;) and the synthetic speech spectrum &Scirc;&ohgr;(&ohgr;) into a plurality of bands B each containing a plurality of frequencies &ohgr;, comparing said original and synthetic speech spectra within each band; and determining a voicing probability for each band on the basis of said comparison.