This achievement is for achieving at least 90% voltage on song number 3 in the list. Voltage is essentially a bit like your hit ratio, so you must hit as many notes as you can during the song.
You can get an idea of how you're doing by the cheer marker on the left of the screen which fills up as you play. It starts off as light blue, then yellow, then orange. Once you fill the orange bar it changes to alternating colours. If the bar is in the last state by the end of the song you're safe, but also filled high with orange can be enough.
Also, this can be achieved on any difficulty so if you are having trouble, you can always just set the song to Easy.