I have been thinking about pipe organs these days and they have given me some food for thought for a few observations.
One only need a brief perusal of the world of organ stops to realize that trying to mimic sounds by mimicking their partials has been with us since the 1st additive synthesizer, the pipe organ.
Pipe organ stops attempt to mimic anything from violins to the human voice by simply trying to physically recreate partials. Truth be sold that attempts to get a pipe organ to sound like a human voice or a violin have been rather feeble.
This brings me to a diamond in the rough, the Kawai K5000. This is a great synth because those who designed it realized what pipe organs would have told them centuries ago. No natural waveform is fixed.
If you want to get something to sound like a certain musical instrument sample it. And yes, I am aware that sampling is passé and old school. Who cares? Certainly not me. The exception to this is physical modeling but that is for another blog.
Its also important to realize that the attack and decay of a sound should be looked at differently that the sustain and release. This is what the K5000 did and it's easy to do with any DAW today by layering (or dare I say modern day orchestration w/o the orchestra).
I also don't really understand spectral morphing. My personal opinion is that trying to morph one instrument into another with additive synthesis is trying to fit a square peg into a round hole. What additive synthesis can do is a lot of spectral Alchemy in the sustained part of the note. It's why I like Alchemy more for pads and soundcapes than instrument sounds. But the partials in the attack transient are non linear, noisy and chaotic not to mention very brief. Trying to morph them just creates artifacts that IMHO are far from musical.
What synths like Alchemy do well is create morphs in the sustained part of the note. This is worth doing. It creates a dynamic spectrum rather the fixed spectrum of a natural instrument during it's sustain which is what synthesis does well.
I think the focus in additive synthesis is in the wrong place. Rather than trying to create modern day organ stops it's far more productive to look to the richly creative world of pads, drones and soundcapes and leave the transient to samplers and physical modelers.