We have experimentally studied the generation of sonoluminescence (SL) and cavitation noise in the field of a focusing ultrasonic radiator during a gradual smooth increase in the applied voltage. In addition to the SL signal, we have recorded the output signal of a hydrophone situated behind the focal region of the radiator and measured the cavitation noise spectrum. Four stages in the development of a cavitation zone have been distinguished as manifested by the specific character of dependences of the measured parameters on the voltage applied to the radiator. Spectral signs of the cavitation noise characteristic of each stage of development of the cavitation zone.
