The inhomogeneous mechanism of band shape formation is considered for XH vibrational modes of hydrogen bonded complexes (AD-H...B. Experimentally observed bands are shown to result from superposition of separate bands corresponding to hot, with respect to low-frequency intermolecular vibrations, transitions. Spectral band shapes are substantially influenced by Fermi resonance between terms of the XH modes and internal vibrations of a proton donor. A number of Fermi resonance between terms of the XH modes and internal vibrations of a proton donor. A number of diverse spectral manifestations of Fermi resonance are predicted (a hole at the internal mode frequency, the appearance of an intense narrow band, intensity redistribution between separate parts of a contour, etc), and their dependence are examined on magnitudes and signs of matrix elements determining unperturbed band intensities, as well as on the matrix element of an anharmonic part of the Hamiltonian.