Diatonic accordions contain one to three treble rows and eight basses, wherein only notes from diatonic scales may be played, without changing keys; on the contrary, bass side chord roots include chord root notes with several key accidentals as part of each chord structure.
The right hand treble keyboard contains several switches (also referred to as couplers or registers) which activate different sets of reeds, producing an abundance of sounds and timbres.
Keys
Diatonic accordions use one set of buttons which produce identical notes when they are pressed, restricting their playing to certain keys only.
Chromatic button accordions offer more complex chords than diatonic accordions due to their multi-row layout of treble keys arranged chromatically – with fourth and fifth rows duplicating first and second rows for an efficient keyboard layout.
One key difference between diatonic and chromatic accordions is their use for different notes in their range: diatonic accordions require two reeds for every note they produce on press/draw while their chromatic counterparts need only one reed per key/button, making the latter larger and heavier than its diatonic counterparts; an example is Swiss folk music’s popular use of the Schwyzerorgeli bisonoric diatonic accordion as an example of one type of diatonic accordion.
Reeds
One row diatonic accordions, melos deons and German style instruments contain only a ten button row as their keyboard. This provides twenty notes – ten from both “in” and “out” bellows – while bass buttons on either side may change pitch depending on bellows direction – however most instruments use standard patterns of four to twelve bass notes with predictable pattern.
Contrasting with piano and some other diatonic accordions that only include notes from certain scales, chromatic accordions have all sharps and flats as they vary pitch with bellows direction changes. A double action chromatic accordion may also be known as a bayan (bowed).
Melodeons can be tuned either B/C or C#/D; both systems can be successfully used to play traditional Irish music. Some players might prefer B/C as it allows more low keys; however both tunings can be played effectively for this genre of music.
Styles
Diatonic accordions come in many styles, from single row to multiple rows. Most feature left hand chord buttons interspersed with right-hand treble keys played by right hand for that characteristic “um-pa-pa” sound common in European music (check out Youtube tutorials for assistance).
The bass side keyboard produces chords corresponding to those produced by melody buttons, providing chordal accompaniment. Some have unisonoric keyboards such as those found on steirische harmonicika or melodeon instruments while others feature bisonoric keys like those seen in two-row chromatic bandoneon or Schwyzerorgeli instruments.
Some diatonic accordions feature wet tunings for classical and folk music, or swing tuning for lighter sounds; others can have dry tunings specifically tailored for Zydeco or Cajun styles; there are even bisonoric-chromatic instruments such as the oito baixos or gaita.
Accessories
Diatonic button accordions feature a single-action keyboard with one or more rows of buttons that produce notes in diatonic scale when their bellows are pushed or drawn, making this instrument popular for Latin folk music including Norteno, Vallenato and Musette as well as European folk styles, Americana and rock genres.
Two and three row accordions with diatonic note patterns exist as well, such as the Shand accordion named after Scottish accordionist Jimmy Shand. It features three rows of semitone diatonic on its right-hand keyboard and an advanced double action system on its left hand keyboard – for instance, it was recently featured at an accordion convention!
One-row models are popularly employed in Cajun, morris and other Irish music, Quebecois or Breton trad, as well as by players playing Quebecois or Breton traditional. These accordions often have raised buttons and use special tuning not found on regular keyboard accordions (just intonation). B/C or G/C instruments may also be tuned to other keys such as Sol/Do or La/Fa.