Stradella Explorer

How to use

• Choose your instrument size from the buttons at the top. The boards rebuild instantly.
• Combinator — press a Bass or CB button to set your root, then add the chord buttons. The chord name and interval breakdown appear immediately.
• Multiple buttons lighting up at once is normal: enharmonic equivalents of the same root note are all highlighted together.
• Chord Finder — pick a root and a chord quality from the dropdowns. Results appear instantly, ranked by playability. Browse with ◀ ▶ or your keyboard arrow keys.
• Both boards always stay in sync. Mirror View is what you see looking at your own hand; Standard View matches printed charts.
• ▶ previews the sound. Esc resets everything.

Why this calculator exists

Most accordion chord lists you find online quietly ignore a physical fact: every chord button on the Stradella bass sounds inside a single octave. So they print wide jazz voicings — elevenths, thirteenths, altered chords — as if the instrument could stack them the way a piano does. It can't. Follow those charts and you reach for a chord that either doesn't exist on the system, folds into a tight cluster inside one octave, or simply isn't the chord the symbol promised.

This tool was built to be honest about all of it. It lists every chord — including the ones the Stradella can only approximate, the ones whose notes sit close together inside one octave, and the ones that are really something other than their name suggests. Rather than hide those cases, it shows them and explains what you are actually hearing, so you can decide for yourself — a skilled player who separates the hands and voices these deliberately will get plenty out of them.

A complete, truthful reference is more useful than a partial one. Whether you are looking for a voicing that works, checking whether a chord on a lead sheet is even reachable, or just curious about why a button sounds the way it does, the goal is the same: tell you the truth about what the buttons under your fingers really produce, and let you make the call.

What the buttons actually play

The Stradella bass is a grid of buttons in columns, with the rows running through the twelve roots in a circle of fifths; each row is anchored to one root. Depending on size, a row offers some of these columns: counter-bass (the major third above the root, used as a bass note), bass (the root), and the chord buttons major, minor, seventh and diminished.

Each chord button sounds a fixed set of notes inside a single octave. Major and minor are complete triads (root, third, fifth). The seventh button is not a complete four-note seventh chord: it sounds the root, the major third and the flat seventh, with the fifth omitted — three reeds, by design. The diminished button sounds three notes too — see the note at the foot of this section.

Some instruments use a "French" layout for the seventh column, in which the button sounds the third, fifth and flat seventh and omits the root instead of the fifth. The calculator's French toggle switches to this voicing.

Combining bass notes and chords

The Stradella system has no dedicated buttons for extended or altered chords. They are produced by pressing more than one button at once — a bass or counter-bass together with one or two chord buttons.

For example, a C bass played with the E minor chord (C + E minor) sounds a C major seventh. The calculator's Combinator works the same way in reverse: press a combination and it tells you the chord that results.

Why extended chords are acoustic approximations

Every chord button sounds within a single octave. That is the structural limit of the system, and it shapes what extended chords can be.

In a piano or guitar voicing, the extensions — the ninth, eleventh and thirteenth — sit above the basic chord, spread across more than one octave. On the Stradella there is no register to stack them there. The extensions fold back down into the same octave as the chord tones, where they land next to notes they were meant to sit above. A thirteenth folds in as an added sixth; an eleventh lands a tone from the third.

What you hear is therefore an acoustic approximation of the named chord, rather than the full voicing the symbol implies. This is not a fault in the calculator or the instrument; it is inherent to fitting wide harmony into one octave — and used deliberately, with the hands separated, these folded voicings are a real part of the instrument's colour. The coloured notes in the Finder's results flag, case by case, where this folding affects a particular chord.

How the Chord Finder works

The Finder stores no table of fingerings. Every time you pick a root and a quality, it searches the entire board from scratch — and on a 120-bass instrument that is a large search. From the board's 80 chord buttons it builds exactly 1,992 candidate button combinations: all 80 single buttons, plus every one of the 1,912 reachable pairings of two.

Each of those combinations is fully evaluated. The calculator gathers every pitch the buttons produce, reduces them to an ordered interval signature, and matches that signature against a dictionary of 92 chord shapes — then measures the physical span between the buttons in pixels to judge whether a human hand could actually reach them. That is tens of thousands of operations for a single query, completed in the blink of an eye as you change a dropdown.

Two filters then prune what survives. The first drops redundant combinations: if one button already produces the chord, a two-button version that adds nothing is discarded. The second drops the physically impractical ones, whose buttons are spread too far across the board to be played together.

Finally the survivors are ranked: fingerings playable with the exact spelling come first, then those using fewer buttons, then the most compact reaches. This is why a chord can return several ordered options, why some return none, and why the best fingering is always the one shown first.