I'll very likely be getting one of these additive synths soon, but I get lost in trying to compare the major features, partly because the interfaces are fairly complex, and partly because there is no demo for Alchemy yet.
From what I can tell, though:
All three, in a sense, let you create and resynthesize multisamples. Tera has you add the samples in a separate box that's called up when you click on Sample as the oscillator. Alchemy lets you load sample by sample, or import an SFZ multisample. Morphine forces you to load each sample separately, but only Morphine lets you see something similar to a keymap, so you can immediately see what notes you are working on. In the others, you can see the name of the "sample" that you are working on and text indicating its keyrange, but there is no actual map that lets you just click on a zone to start editing it.
But Alchemy creates up to 600 partials per note. The other two are limited to about 125 partials per note.
And Alchemy lets you create multiple velocity zones for each note. Tera lets you only have two velocity zones per note and morph between them. Morphine seems to be the most limited in this respect--only one velocity layer, but it lets you set the velocity response for each partial, so upper partials can be kept quiet on low velocity strikes.
Alchemy and Morphine only show the harmonic partials. Alchemy instead puts the inharmonic\noise sounds into another source. Tera shows more partials, but neither indicates if they are harmonic nor lists the freq of each, so you are flying blind.
In other words, I want a combination of all three of these instruments, since each is limited compared the others.
The wisest choice seems like Alchemy in some obvious respects: the number of partials, the ability to create velocity layers. But not being able to see the keymapping for the resynthesized samples worries me. Trying to edit a complex instrument looks like it will be tedious and prone to human error. And I have to admit that I've played around with editing the default presets in Morphine, and like what it can do--very very easy to move from key zone to key zone and change the partials. Great sound, too. But it's the most limited of the programs in other respects. (Though not very limited, given what it can do...)
So I'm a little lost. I'm ready to dive into one of these programs. Anyone here used two or three of these programs? Are there other big advantages or disadvantages that I've missed when it comes to creating a fairly complex emulation of an acoustic instrument in these programs?