Basslines in popular music often use "riffs" or "grooves", which are usually simple, appealing musical motifs or phrases that are repeated, with variation, throughout the song. Bassline riffs usually emphasize the chord tones of each chord (usually the root note, the third note, the fifth note, and the octave of a chord), which helps to define a song's key. At the same time, basslines work along with the drum part and the other rhythm instruments to create a clear rhythmic pulse.
The type of rhythmic pulse used in basslines varies widely in different types of music. In swing jazz and jump blues, basslines are often created from a continuous sequence of quarter notes in a mostly scalar, stepwise part called a "walking bass line." In latin, salsa music, jazz fusion, reggae,electronica, and some types of rock and metal, basslines may be very rhythmically complex and syncopated. In bluegrass and traditional country music, basslines often emphasize the root and fifth of each chord. Minute rhythmic variations by the bass can dramatically change the feel of a song, even for a simple singer-songwriter groove.
Though basslines may be played by many different types of instruments and in a broad musical range they are generally played on bass instruments and in the range roughly at least an octave and a half below middle C. In classical music, basslines play the same harmonic and rhythmic role; however, they are usually referred to as the "bass voice" or the "bass part."
In some popular music bands, keyboard instruments are used to play the bassline. In organ trios, for example, a Hammond organ player performs the basslines using the organ's bass pedalboard. In some types of popular music, such as hip-hop or house music, the basslines are played using synthesizers, sequencers, or electroacoustically modeled samples of basslines. In electronic music and house music, basslines are often performed on electronic devices such as the Roland TB-303.
In modern popular music, the bassline is generally played by an electric bass guitar player. The bassline bridges the gap between the rhythm part played by the drummer and the melodic and harmonic lines played by the lead and rhythm guitarists. Bass players also perform fills in between the phrases of the vocal melody, and they may also perform bass runs or bass breaks, which are short solo sections.
"In any style, the bass's role in the groove is the same: to keep time and to outline the tonality. When developing bass lines, these two things should always be your goal" (Santerre 2001, p.iv).
Some rock bass guitarists, such as John Entwistle, John Deacon, Chris Squire, Paul McCartney, Phil Lesh, Les Claypool, Flea, Victor Wooten, Geddy Lee, or the more recent Chris Wolstenholme have developed a lead sound, incorporating bass solos along with their rhythm playing. Funk bassists often use slapping and popping, in which the bassline uses a number of percussive muted notes.