Distinct electrotactile stimulation can be used as a method for machine-to-human communication. Distinct sensations can be created through the intensity of the observed electrotactile waveform. Among the possible techniques to modify intensity, this paper investigates the possibility of manipulating a train of high-frequency pulses with the duty cycle of a superimposed mask. Furthermore, this paper explores the limits of human ability to distinguish intensity levels created through manipulation of high-frequency pulses. This paper found that using the presented frequency manipulation technique makes it possible to reliably create 2-3 intensity levels with an accuracy higher than 85%.