Diatonic button accordion

A melodeon or diatonic button accordion is a member of the free-reed aerophone family of musical instruments. It is a type of button accordion on which the melody-side keyboard contains one or more rows of buttons, with each row producing the notes of a single diatonic scale. The buttons on the bass-side keyboard are most commonly arranged in pairs, with one button of a pair sounding the fundamental of a chord and the other the corresponding major triad (or, sometimes, minor triad).

Diatonic button accordions are popular in many countries, and used mainly for playing popular music and traditional folk music, and modern offshoots of these genres.

Various terms for the diatonic button accordion are used in different parts of the English-speaking world.

To simplify matters and avoid ambiguity, in the remainder of this article the term diatonic button accordion, or DBA, will be used.

The following definitions will assist understanding of this article.

Most diatonic button accordions have a "single-action" (or bisonoric) keyboard, ^{[citation needed]} meaning that each button produces two notes: one when the bellows are pressed or pushed (closed) and another when the bellows are drawn or pulled (opened). In this respect, these instruments operate like a harmonica.

(In contrast, most other types of accordion, for example piano accordions and chromatic button accordions, are "double-action" – or unisonoric – because each key produces a single note regardless of bellows direction.)

Other single-action or bisonoric members of the free-reed family include the German concertina, the Anglo-German (or "Anglo") concertina, the bandoneon, the Chemnitzer concertina (see concertina) and the mouth organ (harmonica).