Interface GrooveExtractorEngine

Mode C: a recording instead of a file. The tempo is an argument rather than something read off the signal, because timing is meaningless without it.

Mode A: align two performances of the same material - one played straight, one played - and keep how far each played note sat from its quantized counterpart.

Mode B: one performance and no reference. The notes themselves are projected onto the nearest grid slot, so what comes back is the residual of a played file against its own implied grid - the deviations a straight quantization would remove.