catfact
commented
5 years ago this seems to be rounding error. storing rate and phase as double puts the error back into +/-1 sample index.
leaving open, since it's not nice to have an error at all; needs more testing with long loop times.
(read/write indices are re-synced when a subhead position change happens, e.g. at loop endpoint.)
there is still some drift between read frame index, and write frame index when resampling. it appears rate-dependent.
depending on the rate, the drift is bad enough that the positions cross and we get a glitch:
this shows the difference between read phase (float) and write phase (int). the small variations are expected; the overall sawtooth shape is not. especially bad is that the difference changes sign.