The sample_quality settings from 3 to 10 are interpolations based on the windowed sinc method.
https://ccrma.stanford.edu/~jos/lumped/Windowed_Sinc_Interpolation.html
In the RGC sfz software, we have a number of quality settings available from a drop-down menu.
These sinc settings are labelled: 08 12 16 24 36 48 60 72
One can easily guess that these designate a number of points. The numbers are multiples of 4, which makes them practical for SIMD processing.
For implementation purposes, we want to precompute the sinc function in a large table.
A window must be applied to the windowed sinc, in order to squash the edges.
A Kaiser window is most appropriate, which permits to keep aliasing ripples under a determined amplitude threshold. It has a parameter Beta, permitting to establish a compromise: the higher Beta, the lower is the alias magnitude, but the selectivity of the "brick wall" filter worsens near the cutoff point.
At first it seems an alright choice of Beta may be from about 6 to 10, as table size increases from 8 to 72.
Tool for plotting frequency responses of sinc interpolators dynamically, when size and Beta are varied, based on the deip.pdf paper.