Spectral morphing

Spectral morphing transitions between wavetable frames by interpolating partial amplitudes and phases instead of blending waveform samples directly.

Working per-partial lets the morph follow the harmonic structure of the frames, so brightness, formant shape, and phase relationships travel together instead of canceling. It is the engine behind smoothly evolving, vocal-like sweeps that would sound hollow if the same frames were only crossfaded.