A new frequency domain method for the quantification of glottal volume velocity waveforms is presented in this study. This technique, called Parabolic Spectral Parameter (PSP), is based on fitting a parabolic function to a pitch-synchronously-computed spectrum of the estimated voice source. The PSP-algorithm gives a single numerical value that describes how the spectral decay of an obtained glottal flow behaves with respect to theoretical bounds corresponding to maximal and minimal spectral tilting.