This icon is a part of a collection of Pionowe ustawienia miksera flat icons produced by Icons8. Icons follow the guidelines of iOS, Windows, and Android and are designed by a single designer, guaranteeing the consistent quality. Both PNG and vector are available.
It's an image of three vertical analog equalizer sliders arranged side by side. The slider knobs are all in different positions vertically to indicate different selection of base, mid, and treble. It is three vertical lines each with one rectangular knob.