A spectral approach is proposed for voice source parameters representation and estimation. Parameter estimation is based on decomposition of the periodic and the aperiodic components of the speech signal, and on spectral modelling of the periodic component. The paper focusses on parameters estimation for the periodic component of the glottal flow. A new anticausal all-pole model of the glottal flow is derived. Glottal flow is seen as an anticausal 2-pole filter followed by a spectral tilt filter. The anticausal filter has complex poles, instead of the real poles that are usually assumed. Time-domain and frequency domain parameters are linked by analytic formulas. Two spectral domain algorithms are proposed for estimation of open quotient. The first one is based on measurement of the first harmonics, and the second one is based on spectral modelling. Experimental results demonstrate the accuracy of the estimation procedures