Cubic Infinite Linear Oversampling
tanh(a x) with cubic infinite linear oversampling
This is a small improvement (?) to Efflam Le Bivic's excellent 'Infinite Linear Oversampling' core macros. This method employs cubic spline interpolation to further reduce aliasing artefacts. Demonstrated is tanh(a x) both in it's original ILO, and cubic interpretation. The spline points are set to be 1 sample apart here, although, obviously, this can be altered to however you see fit for your purposes. Due to the nature of spline interpolation, delay performance is not er as performant as the original ILO.
CPU usage is slightly more then four times greater than original ILO processing. Sound quality improvement is small but definitely noticeable, and quite clearly visible on an FFT display.
I hope this is useful for someone.