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I recently tested, reed by reed, exactly which note(s) each bass button plays on my accordion.

I did this so I have a better understanding of what I am dealing with when playing.

What I found was confusing.

The basics:

There are 12 reeds in a lower octave for bass notes and 12 in a higher octave for chords, both A–G#.

Each bass button also plays its chord counterpart reed. For example, the C bass button will open 2 C reeds.

The illogical part: The octaves.

A–B span 2 octaves (24 semitone interval) C–G# span 1 octave (12 semitone interval)

For example, A bass plays A2+A4, but C bass plays C3+C4.

This means that A–B are higher AND lower than C–G#.

With a coupler A1–B1 and A3–B3 get added as well. So you would think this solves the problem, however only C2–G#2 get added.

So A–B are higher AND lower even with the coupler.

What is the logic behind this? The accordion is old, like probably 100 years. Could it be a tuning problem (by whole octaves? is that even a thing?)?

2 Answers 2

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It's likely intentional. Other accordions with a Stradella bass do similar tricks to make bass scales sound smoother.

When playing an ascending scale using one voice and a single octave range, at some point the voice will jump down a seventh in order to stay within the range. But when you have multiple voices that are octaves apart, each voice can enter or exit at a different point in the scale, smoothing this over. This results in a sort of barber-pole effect: each step sounds like an ascending interval, but you end up back where you started.

Without the coupler, when going from G# to A, the top voice continues upward and the bottom voice jumps down, which is less abrupt than both voices jumping down at the same time. For transition from B to C, the bottom voice continues upward when the top note jumps down.

With the coupler, the lowest bass voice enters at the transition from G# to A, while the other three voices go up a half step. At the transition from B to C, the top voice cuts out, while the other three go up a half step.

This should sound more like going up a half step than going down a major seventh. It will be difficult for most listeners to tell exactly which octave(s) a bass button uses. (They might not notice that the bass plays octaves at all.)

Although we don't often play entire bass scales other than as an exercise, we do often play parts of a scale and it's nice if there isn't an obvious jump in the middle. It should also be somewhat true of other arpeggios; if you place C-E-G-C then the last C is the same as the first, but it might not be so easy to tell which is the jump down, making it a reasonable substitute for a multi-octave bass instrument where the last C actually is up an octave.

Compare with Shepard tones. More here.

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Your analysis is missing the multiplicity of the notes when the octave wraparound occurs in one reed bank.

In general, a Stradella bass is structured into bass reed banks and chord reed banks, with each reed bank containing 12 contiguous semitones. When you press a chord button, it is translated into 3 notes (old instruments may have 4 notes on some chords), and all chord reed banks selected by the current bass register will sound those notes in the octave they have available.

When you press a bass button, it sounds the bass note in all selected bass reed banks (again, in the individual octave that the reed bank has available), and in almost all modern instruments also all chord reed banks so that the bass notes

a) have punch compared to the chords b) have a rather fuzzy octave

Now there are different schools of how to best mask octave breaks. An older Morino (or Morino Artiste) with 5-reed bass has bass reed banks starting at E1 and E2, and chord reed banks starting at E3, E4, and E5. Very straightforward, no duplicate notes.

A typical Italian 5-reed bass may have bass reed banks starting at A1 and A2 and chord reed banks starting at F♯3, C4, and C5. The lowest chord reed bank has notes overlapping with the middle chord reed bank, and notes overlapping with the higher bass reed bank. When you are playing bass runs, there are actually 3 different octave breaks within the 12 notes you have available, making each of them comparatively inconspicuous.

Each bass button will sound the same number of reeds as any other, but not the same number of different notes/octaves as every other button because of that overlap.

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