Rock 'n' roll developed in the mid-twentieth century as a combination of other genres, such as blues, country, and jazz. Despite its eclectic origins, the music was usually stripped down, featuring limited combos. The typical instrumentation of a rock combo is one or more guitars, electric bass, drums, and occasionally a piano, organ, or horns.

The time signature is two numbers, which are stacked one on top of the other and are placed at the beginning of a piece of music. The top number indicates how many beats are in each measure. The bottom number indicates how long each beat will last, with a four meaning a quarter more, and an eight an eighth note.

The eighty-eight notes on a keyboard are produced by pressing white and black keys. The black keys are positioned slightly higher and farther back, as they hold all of the sharp and flat notes on the twelve-tone chromatic scale. This arrangement allows the natural notes to be played more easily, and make the non-natural notes more obvious.

In musical notation, the note "piano" above a clef indicates that the music should be played softly. Often such a mark, sometimes abbreviated with just a "p," will come in the middle of a piece to indicate a change of volume. The opposite notation is "forte," which indicates that the music should be played loudly.

Although configured and played quite differently, both the accordion and the harmonica produce sound by having air blow over free reeds. While the accordion has buttons to open and close specific reeds, a harmonica player blows over a specific hole to create the desired tone.

While the term Neoclassicism typically refers to the Enlightenment trends that focused on ancient Greece and Rome, in music the term refers to twentieth-century music that looked back to the "Classical" music of the eighteenth century. The composers Igor Stravinsky and Alfredo Casella were important figures in this movement.

In the early twentieth century, many composers sought to go beyond the traditional eight note scale of Western music. The first composer to set out a system to use atonality in compositions was Arnold Schoenberg, who created a "twelve tone system" in the 1920s of chromatic tones that gave each note equal weight. The system was used heavily by composers after World War II.

A mandolin is tuned exactly like a violin, but with one key difference. Instead of having one string each tuned to G, D, A, and E, the mandolin has two courses of strings tuned in unison to each of these notes. The mandolin shares this trait with the entire "mando" family, including the mandola and the mandocello.

The Young Person's Guide to the Orchestra was conceived as a multi-media piece to educate children about orchestra music. Benjamin Britten's adaptation of the work of Henry Purcell, however, showed such great arrangements and inventiveness of instrumentation that it was immensely popular as an orchestral piece and record.

Accordions have been used in a wide variety of traditional folk music around the world. Accordions, free reed instruments that can be played with either a keyboard or diatonic buttons, provide a multitonal and varied sound that can accompany a voice all on its own. One notable exception to the kind of folk music that features the accordion is bluegrass, a folk style developed in Appalachia that exclusively features string instruments such as the guitar, banjo, fiddle, dobro, and mandolin.