Having trouble getting my lagrange 4-point interpolator to function properly. Harmonics are being generated from somewhere, possibly due to the amplitude exceeding FSD (DC offset?). When I then include it in my waveguide, as soon as DSP is enabled, pd beeps, and then leaves crackly noise/fuzz regardless of whether the patch is being fed an audio signal or not. Remove the FIR filters, and it functions again as normal.

Interested to know how others have achieved fractional delay filters within pd, be it Lagrange or Thiran Allpass for example.

Patch is attached, "FIRTest.pd" is the parent patch.

Any help would be greatly appreciated.

Aaron