Our physical body can only feel up to 1,000Hz. Healy can provide much higher ranges and each program delivers different ranges of freqencies, measured in Hz. You can try to increase the intensity until you feel a slight tingle. Some of us are more sensitive than others. On some days you may resonate more with some frequencies, on some days less. It also depends on whether the program has current control or voltage control. The ear electrode programs usually use current control, meaning that the voltage is variable until a certain current level is reached. Often the current intensity is very low, and you cannot feel the current, because less current is needed for cranial application.