We present a study of the alternating voltage generated in YBa 2 Cu 3 O 7−␦ ͑YBCO͒ tapes in response to sinusoidal magnetic fields applied perpendicular to the tapes. The alternating field induces a strongly nonlinear voltage response with various waveforms that drastically change upon changing the bias current, the bias magnetic field, and the amplitude and frequency of the alternating field. In particular, one observes transitions from waveforms including double peaks to waveforms including a single peak in one cycle of the alternating field. We attribute these effects to modulation of the vortex pinning energy by both the alternating magnetic field and the alternating current induced by it. Our model allows separation of these two contributions to the total response, thus revealing the dominating source of the nonlinear response and its accompanied steady component at different experimental conditions.