Energy shifts of radiation from accreting black holes may be caused by the fast orbital motion and the gravitational redshift near the event horizon. Individual clumps of matter experience the effects of general relativity as they gradually fall into a deep potential well. An episodic supply of material is maintained by tidal disruption events and the emerging radiation is modulated in the X-ray domain and in longer wavelengths. Changes of polarization properties of the observed signal exhibit a specific dependence on energy and phase.