Thank you, you have found a bug in the delay operator for @interp spline6! I've dug into this and found the culprit (a typo), and there's a fix checked in for code review and inclusion in the next update hopefully (ticket #13572)
In the meantime, if you need @interp spline6, it *is* working fine for the sampler operators (sample, peek etc.) and for the interp operator (interp @mode spline6) -- and there's a codebox equivalent in the gen~.interpolation example patcher; you could perhaps use one of these to implement the equivalent of delay @interp spline6 until the update fix is released.
Hi again Graham,
While I'm a it: the reason why I was experimenting with interpolations is that I'd like to reproduce exactly the behavior of tapin/tapout in gen~. But as far as I know, tapout~ is performing a 4-point Lagrange interpolation, is it correct? If yes, would it be possible to implement also 4-point Lagrange in the delay operator?