The Stradella Bass System (sometimes called standard bass) is a buttonboard

Button (control)

A push-button or simply button is a simple switch mechanism for controlling some aspect of a machine or a process. Buttons are typically made out of hard material, usually plastic or metal. The surface is usually flat or shaped to accommodate the human finger or hand, so as to be easily depressed...

 layout equipped on the bass side of many accordions, which uses columns of buttons arranged in a circle of fifths

Circle of fifths

In music theory, the circle of fifths shows the relationships among the 12 tones of the chromatic scale, their corresponding key signatures, and the associated major and minor keys...

; this places the principal major chords of a key (I, IV and V) in three adjacent columns. Each column contains, in order:

• The major third
  Major third
  In classical music from Western culture, a third is a musical interval encompassing three staff positions , and the major third is one of two commonly occurring thirds. It is qualified as major because it is the largest of the two: the major third spans four semitones, the minor third three...
  
   above (or minor sixth below) the root ("counter-bass")
• The root note
  Root (chord)
  In music theory, the root of a chord is the note or pitch upon which a triadic chord is built. For example, the root of the major triad C-E-G is C....
  
  
• The major chord
  Major chord
  In music theory, a major chord is a chord having a root, a major third, and a perfect fifth. When a chord has these three notes alone, it is called a major triad...
  
  
• The minor chord
  Minor chord
  In music theory, a minor chord is a chord having a root, a minor third, and a perfect fifth.When a chord has these three notes alone, it is called a minor triad....
  
  
• The dominant seventh chord
• The Diminished seventh chord
  Diminished seventh chord
  A diminished seventh chord is a four note chord that comprises a diminished triad plus the interval of a diminished seventh above the root. Thus it is , or enharmonically , of any major scale; for example, C diminished-seventh would be , or enharmonically...
  
  

The following chart shows a standard 120-button Stradella layout.

In modern accordions, each chord button sounds three individual pitches. Early accordions sounded four pitches for the seventh and diminished chords. Modern Stradella systems omit the 5th from these two chords, allowing for more versatility. For example, an augmented seventh chord can be created by using the dominant seventh chord button and adding an augmented 5th from the right-hand manual or from one of the bass or counterbass buttons.

In most Russian layouts the diminished seventh chord row is moved by one button, so that the C diminished seventh chord is where the F diminished seventh chord would be in a standard Stradella layout; this is done in order to achieve a better reachability with the forefinger.

Register switches

The larger and more expensive accordions can also have on the Stradella bass side, some Register switches, similar in concept to the treble register switches

Accordion reed ranks & switches

A reed rank inside accordions refers to a single full set of the reeds that are the means to achieve the instrument's sound range. These reed ranks are located in the reed chamber...

Common configurations

Name	Columns	Rows of bass-notes	Rows of chords
8-bass	4 - Root notes: F to D	Root note	Major
12-bass	6 - Root notes: B♭ to A	Root note	Major
24-bass	8 - Root notes: E♭ to E	Root note	Major, minor
32-bass	8 - Root notes: E♭ to E	Root note	Major, minor, 7th
40-bass	8 - Root notes: E♭ to E	Major 3rd note, root note	Major, minor, 7th
48-bass	8 - Root notes: E♭ to E	Major 3rd note, root note	Major, minor, 7th, diminished
	12 - Root notes: D♭ to F♯	Major 3rd note, root note	Major, minor
60-bass	12 - Root notes: D♭to F♯	Major 3rd note, root note	Major, minor, 7th
72-bass	12 - Root notes: D♭ to F♯	Major 3rd note, root note	Major, minor, 7th, diminished
80-bass	16 - Root notes: C♭ to G♯	Major 3rd note, root note	Major, minor, 7th
96-bass	16 - Root notes: C♭ to G♯	Major 3rd note, root note	Major, minor, 7th, diminished
120-bass	20 - Root notes: Low A to A♯	Major 3rd note, root note	Major, minor, 7th, diminished
140-bass	20 - Root notes: Low A to A♯	Major 3rd note, root note	Major, minor, 7th, diminished, augmented
160-bass	20 - Root notes: Low A to A♯	Three major 3rd rows, root note	Major, minor, 7th, diminished

See also

• Array system, same circle of fifths
  Circle of fifths
  In music theory, the circle of fifths shows the relationships among the 12 tones of the chromatic scale, their corresponding key signatures, and the associated major and minor keys...
  
   system for an mbira
  Mbira
  In African music, the mbira is a musical instrument that consists of a wooden board to which staggered metal keys have been attached. It is often fitted into a resonator...
  
  
• Alternate bass
  Alternate bass
  In music, alternate bass is a performance technique on many instruments where the bass alternates between two notes, most often the root and the fifth of a triad or chord....