Two instruments sharing one bellows
An accordion’s treble side is a chromatic keyboard — piano keys or buttons, one note each, unisonoric on a standard piano accordion so the same key sounds the same note whether you push or pull. The bass side is almost the opposite: on the near-universal Stradella system, most buttons don’t play a single note at all — they trigger a pre-wired chord. “In tune” on an accordion means every reed behind both sides agrees with itself, and there are usually hundreds of them.
Play a reference tone, then play the matching key on a single-reed register and compare on the dial above. Extreme high keys may not reproduce well on phone speakers — trust the dial over your ears there.
Where the pitch actually comes from
Every note is a steel reed— a thin tongue riveted at one end over a slot, set vibrating by bellows air. There is no peg, pin or screw anywhere in the signal path. The only way to change a reed’s pitch is to remove metal from it with a file: thinning the free tip makes the tongue lighter and raises the pitch; thinning near the fixed base makes it more flexible and lowers it. That change is permanent, which is exactly why this page is built around measuring rather than adjusting — filing is a trade skill covered in full in our accordion tuning guide.
Most notes are actually two reeds, not one: a separate tongue for bellows push and another for pull, mounted on the same plate. They age independently, which is why the dial can read differently in each direction on the same key.
Checking reed pitch, step by step
- Pick a single-reed register first.Use the switches above the keyboard to select a voice marked “clarinet” or “bassoon” (one reed rank) rather than “musette” or “violin” (two or three ranks sounding together). Measuring a multi-reed voice measures the deliberate detuning covered below, not the reed itself.
- Play with light, steady bellows pressure. Hard bellows pressure bends a reed flat by several cents — the same reed can read differently depending on how hard you push. Use the gentle pressure of normal playing and keep it consistent note to note.
- Check both push and pull on notes that matter to you. A note clean on the draw and sour on the press has told you exactly which of its two reeds needs work.
- Look at the pattern before judging any single note. If everything reads the same number of cents off, your accordion is consistent with itself and likely tuned to a different reference pitch entirely (see the FAQ below) — not actually out of tune.
Treble layouts, bass systems and bisonoric boxes
The 41-key piano keyboard above is the most common right-hand layout, but plenty of accordions use button keyboards instead (the C-system or B-system chromatic layouts), covering the same chromatic range across diagonal rows rather than piano keys — the tuner reads either the same way, note by note.
On the bass side, the Stradella system stacks six rows: a counter-bass row, a fundamental bassrow of single notes, then major, minor, dominant-seventh and diminished-seventh chord rows. The fundamental row is arranged in the circle of fifths — moving one button typically shifts the bass note by a fifth, not a step, which is why the layout looks scrambled to anyone expecting a scale. Smaller and travel accordions cut this system down (96, 72, 48 or 32 buttons instead of the full 120) by removing the outer rows first, not by changing the layout’s logic. Serious classical players sometimes use a Free Bass system instead, which trades the pre-wired chords for individual chromatic notes across the whole bass side — closer to a second treble keyboard than to Stradella.
One more variant is worth knowing before you assume your reading is wrong: diatonic button accordions (melodeons, and most Irish, Cajun and Tex-Mex boxes) are bisonoric — the same button plays a genuinely different note on the push than on the pull, on both the treble and bass side. If that describes your instrument, seeing two different note names on the same button is correct behavior, not a tuning fault.
Musette tremolo: the “out of tune” that’s on purpose
On most accordions, two or three reeds per note are deliberatelytuned a few cents apart. Engaging a register that sounds them together makes the volume pulse — the shimmering tremolo that says “accordion” the instant you hear it. This is equal temperament with a controlled, intentional error stacked on top, and the amount is a matter of regional style:
| Detune | Common name |
|---|---|
| 0 cents | Dry / unison — jazz, classical |
| ~4 cents | Swing — gentle shimmer |
| ~10 cents | American / Cajun — unmistakable tremolo |
| ~18–25 cents | French musette — the Paris café sound |
This is why “fixing” a musette register to read zero on every reed would ruin the sound the instrument was built for — the wetness is the tuning. Our guide to cents covers how to interpret the offsets this dial reports, and the full accordion tuning guide has a lab you can use to hear each of these detune amounts on its own.
Frequently asked questions
Why does the needle wobble or refuse to settle, even on a healthy accordion?
Almost certainly your register switch has more than one reed engaged. Most voices marked “musette,” “violin” or “tremolo” sound two or three reeds per note deliberately tuned a few cents apart — the tuner hears all of them at once and hunts between them. Switch to a single-reed voice (often marked “clarinet” or “bassoon”) and the needle should settle cleanly if the reeds themselves are healthy.
Is concert pitch on an accordion 440 Hz or 442 Hz?
It depends on the instrument. Many modern accordions are set to A4 = 440 Hz, but plenty of older and European-made instruments — especially French musette boxes — were tuned a touch higher, at 442 or above. Check several notes on a single-reed voice before concluding anything is wrong: if every note reads the same number of cents sharp, your accordion is internally consistent and simply tuned to a different reference than 440.
Can I actually retune my accordion using this page?
No — this tuner measures, it doesn’t adjust. An accordion reed’s pitch is set once, permanently, by filing metal off a steel tongue; there’s no peg or screw this dial can guide you to turn. What this page is genuinely good for is building the tuning chart a technician would start from, or deciding whether a technician is even needed. Our full guide to tuning an accordion covers the filing itself.
The same note reads different cents when I push the bellows than when I pull. Is that a fault?
Not necessarily — push and pull sound two entirely separate reed tongues on the same plate, and a gap of a cent or two between them is normal wear. A gap of ten cents or more names exactly which tongue needs attention. If you play a diatonic (button-box) accordion rather than a piano accordion, push and pull give different notes altogether on the same button — that’s the instrument’s design, not a tuning problem.