Rhythm guitar is the use of a guitar to provide rhythmic chordal accompaniment for a singer or other instruments in a musical ensemble. In ensembles or "bands" playing within the country, blues, rock or metal genres (among others), a guitarist playing the rhythm part of a composition supports the melodic lines and solos played on the lead instrument or instruments, be they string, brass, wind, keyboard or even percussion instruments, or simply the human voice.
In the most commercially available and consumed genres, electric guitars tend to dominate their acoustic cousins in both the recording studio and the live venue. However the acoustic guitar remains a popular choice in country, western and especially bluegrass music, and is used almost exclusively in folk music.
A guitarist "playing rhythm" plays a sequence of chords or arpeggios which embody the chord progression or "changes" that support the melody lines performed by the other instruments or voices. In contrast, the role of the lead guitar is to provide melody, countermelody and solos.
In rock music, the most common way to construct chord progressions is to play "triads", each comprising a root, third and fifth note of a given scale, or four-note chords, which include the sixth, seventh or ninth note of the scale. In some cases, the chord progression is implied with a simplified sequence of two or three notes, sometimes called a "riff", that is repeated throughout the composition. In heavy metal (or just "metal") music, this is typically expanded to more complex sequences comprising a combination of chords, single notes and palm muting. The rhythm guitar part in compositions performed by more technically oriented bands often include riffs employing complex lead guitar techniques. In some genres, especially metal, the audio signal from the rhythm guitar's output is often subsequently heavily distorted by overdriving the guitar's amplifier to create a thicker, "crunchier" sound for the palm-muted rhythms.
In bands with two or more guitarists, the guitarists may exchange or even duplicate roles for different songs or different sections within a song. In those with a single guitarist, the guitarist may play lead and rhythm at different times or simultaneously, by overlaying the rhythm sequence with a lead line. A recent innovation is the use of a "looping pedal" to record a chord sequence or riff over which the lead line can then be played, simulating the sound achieved by having two guitarists.
While rhythm guitarists in metal bands use distortion effects, they tend to use less of the modulation effects such as flangers used by lead guitar players. Whereas the lead guitarist in a metal band is trying to make their solo tone more prominent, and thus uses a range of colorful effects, the rhythm guitarist is typically trying to provide a thick, solid supporting sound that blends in with the overall sound of the group. In alternative rock and post punk bands, though, where the band is trying to create an ambient soundscape rather than an aggressive Motörhead-style "wall of sound", the rhythm guitarist may use flanging and delay effects to create a shimmering background.