If the bars are "full" or pegged at the top, the signal is clipping; on your playback device (phone, PC, or MP3 player).
from E-Stim Systems allow users to connect an audio source (like a phone or PC) via a 3.5mm jack. The device then uses the mode to convert the left and right audio channels into sensations for Channel A and Channel B of the power box. What Makes a "Top" Audio File? estim 2b audio files top