Beating curves

Why a curve at all

Without a curve the app can only tell you how far a reed sits from the bare scale. That is not the same question as whether it is right. A musette is supposed to beat; the curve is where you say how much, and where.

With no curve the goal is flat zero across the range - which is a complete and honest answer, not a missing one. Every reed is then read against the scale itself, which is exactly what you want for a 16', a 4' and the whole bass side, because those are tuned clean.

Typing one: the Btng column

You do not type reeds. You type one beating per note, and the app works the reeds out from it: the reed you put on zero stays at pitch, and the others spread either side.

The number you type is the beat between one reed and the next, which is the number a tuning is named by. Three reeds at 2 Hz sit at −2 / 0 / +2 - each neighbouring pair beats at the 2 Hz you asked for. The outermost pair then beats at 4, which is real and audible, but it is not the figure anyone quotes.

This matters more than it looks. Read it as the full width and you would type 2 expecting 2, and get 4 - twice the tremolo, on the whole instrument, and you would not find out until you heard it.

Nothing assumes three reeds. Any count spreads the same way, one step of the typed value between each neighbouring pair.

Only a few notes

Type a handful and the rest are worked out. Three checkboxes say how, and each one takes a guess away:

• Interpolate - a note between two entries ramps between them. Off, it steps to the nearer one.
• Extrapolate left / right - a note past the outermost entry holds that entry's value flat. Off, it reads zero there.

All three are on by default. The graph draws anything beyond your entries as a dashed line, so you can always see which part of the shape is yours and which part the app is filling in.

The reed on zero

Which reed sits at pitch is yours to choose. A common musette layout is minus / zero / plus, with the middle reed at pitch - but that is a convention, not a law, and nothing in the app assumes it. You can also choose none, in which case the tremolo still has to hang off something and reed 1 anchors it.

Asymmetricity

Where the reed on zero sits inside the tremolo. It never widens what you typed; it only moves you within it. Three reeds, reed 2 on zero, 2 Hz typed:

The outermost reeds stay 4 Hz apart throughout. That is the point: the number you typed stays the number you hear. It is read when the next beating is entered, so it does not move anything already derived.

Cents or hertz

Type in either. It is stored in cents whichever you choose, so the choice is about your hands, not the data.

The view on the graph is a separate switch and changes nothing but the shape of the lines. Both are worth looking at: a musette curve is fairly flat in cents and climbs steeply in hertz, because a fixed cent offset is a growing hertz offset as you go up. Being able to see both without retyping anything is the whole reason there are two.

Fitting one to the instrument

Most technicians do not follow a named school, and most accordions have a tremolo nobody wrote down. So rather than assuming a shape, fit the curve to what the instrument already does: record a pass and let the app compute the trend.

It tells you how many readings it used and how many reeds sit off the instrument's own trend. Those outliers are the point of the fit, not a footnote - they are the reeds the accordion itself says are wrong. If notes were left out because their reeds could not be told apart, it says that too, rather than quietly fitting to two thirds of the keyboard.

This is also how you copy one instrument's tuning onto another.

Show recorded

Overlay the pass on the graph and drag the curve through the dots. The dots are what the accordion does; the line is what it should do. Both are cents from the scale, so they are in the same space and the check is one you can make with your eyes.

A merged pair is drawn as a ring rather than a dot, and named rather than printed as a figure - those are lobes of one peak, not a reed each. The note keeps its place, because dropping it would say nothing was recorded there, which is a different and false claim.

Sharing a curve

A curve belongs to a session, and a session is a file. Copy the file and you have copied the curve, the passes, and the instrument it belongs to. You can also import a curve on its own, from another session.