FretFocus: design recovery for luthiers

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FretFocus home About FretFocus

Try these sample simulations:

  • No construction or measurement error
  • Best rule
  • 17.817 rule
  • 17.835 rule
  • No construction error, measurement s.d. 0.005
  • Best rule
  • Construction s.d. 0.050, measurement s.d. 0.005
  • Best rule
  • 17.835 rule
  • The FretFocus simulator

    To make it easier to get experience with how FretFocus behaves depending on the kind of data coming in, FretFocus has a simulator mode. In this mode, FretFocus will not allow entries in the Value column. Instead, as soon as you enter a Low Fret, High Fret, and inside/outside measurement type, the simulator supplies the corresponding measurement from a simulated instrument that can be configured. FretFocus uses the simulator-supplied entries the same way it uses real entries from you to fit a solution to the data.

    In addition to the scale length, frets per octave, nut compensation, and fret width, the simulator also lets you configure:

    Number of frets
    The simulator calculates the fret positions for the given number of frets. Asking for measurements at higher fret numbers won't work.
    Calculation method
    The simulator will lay out fret positions by one of three methods: the best available (in Java double precision), or one of two common luthier approximations, 17.817 or 17.835, so you can see how one of these approximations used in construction would affect FretFocus's analysis of an instrument. (More about the calculation methods.)
    Standard deviation in construction
    To model the realities of fabricating a real fretboard from wood and wire, the simulator applies a standard deviation for construction. The location for each fret is computed precisely and then offset by a small random amount with a normal distribution and the given standard deviation to find the ‘actual’ location for the fret. These locations are all computed once when the simulator starts and then remain fixed, to model the finished fretboard.
    Standard deviation in measurement
    To model the uncertainty of measurement, each measurement the simulator supplies is precisely computed from the finished fretboard model and then offset by another normally-distributed random amount with the given standard deviation of measurement. Unlike the construction deviation, applied once at startup, this is applied for every measurement: if you get a simulated measurement at two frets, drop it, and ‘measure’ the same frets again, the value will be slightly different each time.

    Either standard deviation, or both, can be set to zero, to see how FretFocus would perform on an instrument that could be built or measured perfectly. With both set to zero, you can also use the FretFocus simulator as a sort of overkill fretboard calculator, where you set the scale parameters and it gives you the distance between any pair of frets.

    Custom simulations

    For the moment, FretFocus does not have an exposed user interface to set up the simulator with custom values. To set up a new simulation, you can copy one of the existing simulation HTML files from the sidebar of this page, and edit it to change the simulator parameters. Comments in the HTML will show you what to change.

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