3-row diatonic button accordion

Introduction
The three-row diatonic button accordion is a popular form of bisonoric accordion which has three rows of buttons for the treble, and typically twelve bass buttons.

History
In the early 19th Century several forms of mouth organ were developed in Europe, similar to the sheng of ancient and modern China or the kaen of Thailand. The next major development was the addition of bellows. Among the most important early developments of bellows-blown free reed instruments was the English concertina. This was a fully chromatic instrument which soon became popular in the classical concert hall. The related German concertina and Anglo-German concertina adopted the in-out scale of the recently invented diatonic harmonica, which made it relatively simple to play melodies and accompanying rhythmic chords.

The earliest accordion was designed to simply play chords. From this evolved the diatonic button accordion that has chord and bass buttons for the left hand and keys in the scale of the harmonica or Anglo-German concertina for the right hand. The three-row diatonic accordion is one of these with rows of buttons for each of three keys.

International System
The most common layout was developed by Hohner and is sometimes called the International System, because it is widely used in accordions around the world. The Tex-Mex button accordion uses this three-row button layout, and is popular in Conjunto and Norte&ntilde;o groups. It is also popular for use in Zydeco music. The International System has the rows in, for example, G, C, and F, from lowest to highest key, which enables, by cross fingering to play the same notes on push and pull. They are available in other keys, but always at these intervals. A primary advantage of this is that one is no longer required to play in a bouncy style as on a single-row melodeon. At the end of the rows of notes are accidentals that are useful in playing some tunes and in some keys.

Though accidentals are available, making a chromatic scale technically possible, there are not enough chromatic notes and not enough on both pull and draw to make chromatic playing practical on this instrument. Nevertheless this system opens up many possibilities not found on a smaller diatonic instrument.

Other Systems
Three-row diatonic accordions can be made in any three keys, and not just in the intervals of the International System. Another pseudo-chromatic layout is a C/C# accordion with an added row for the key of B, thus it is a B/C/C# instrument. These are often made with full Stradella bass system.