A DJ controller is a hardware device used to control DJ software on a computer, tablet, or phone. It allows DJs to physically manipulate digital music similarly to how they would work with turntables or CD players, providing much more precise and intuitive control than a mouse and keyboard. Its main elements are usually two jog wheels, known as "jogs." These wheels simulate the movement of a vinyl record and are used for scrolling through a track, slowing down or speeding up to match the rhythm, which is called beatmatching, or for a technique called scratching. Between the wheels is a mixer section, which contains sliding controls, known as "faders," for adjusting the volume of individual channels and a "crossfader" for smooth transitioning between two tracks. Furthermore, there are rotary knobs for sound equalization—adjusting the bass, mids, and highs—and for controlling sound effects. Modern controllers are often also equipped with pads, which are square buttons used to trigger preset points in tracks, known as "hot cues," samples, or loops. Most DJ controllers have a built-in sound card, also referred to as an audio interface. This allows for connecting headphones to cue the next track while simultaneously sending the main audio output to the speakers. As a result, a DJ controller consolidates the functions of two players and a mixer into a single device for working with a digital music library.