  The estimation of glottal flow from a speech waveform is a key method for
speech analysis and parameterization. Significant research effort has been made
to dissociate the first vocal tract resonance from the glottal formant (the
low-frequency resonance describing the open-phase of the vocal fold vibration).
However few methods cope with estimation of high-frequency spectral tilt to
describe the return-phase of the vocal fold vibration, which is crucial to the
perception of vocal effort. This paper proposes an improved version of the
well-known Iterative Adaptive Inverse Filtering (IAIF) called GFM-IAIF.
GFM-IAIF includes a full spectral model of the glottis that incorporates both
glottal formant and spectral tilt features. Comparisons with the standard IAIF
method show that while GFM-IAIF maintains good performance on vocal tract
removal, it significantly improves the perceptive timbral variations associated
to vocal effort.
